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Pantograph system of high-speed trains become significant source of aerodynamic noise when travelling speed exceeds 300 km/h. In this paper, a hybrid method of non-linear acoustic solver (NLAS) and Ffowcs Williams-Hawkings (FW-H) acoustic analogy is used to predict the aerodynamic noise of pantograph system in this speed range. When the simulation method is validated by a benchmark problem of flows around a cylinder of finite span, we calculate the near flow field and far acoustic field surrounding the pantograph system. And then, the frequency spectra and acoustic attenuation with distance are analyzed, showing that the pantograph system noise is a typical broadband one with most acoustic power restricted in the medium-high frequency range from 200 Hz to 5 kHz. The aerodynamic noise of pantograph systems radiates outwards in the form of spherical waves in the far field. Analysis of the overall sound pressure level (OASPL) at different speeds exhibits that the acoustic power grows approximately as the 4th power of train speed. The comparison of noise reduction effects for four types of pantograph covers demonstrates that only case 1 can lessen the total noise by about 3 dB as baffles on both sides can shield sound wave in the spanwise direction. The covers produce additional aerodynamic noise themselves in the other three cases and lead to the rise of OASPLs.

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... The size of 40 D in the stream-wise direction and 20 D in the corresponding normal direction is employed. In addition, considering the computational resources due to the large amount of mesh brought about by the experimental spanwise length, here the spanwise length is chosen as πD according to references [13,[28][29][30]]. ...

... To make y+ values meet the requirement and y + < 1 in this paper; the first layer thickness is 0.004 mm and the growth ratio of 1.1 is given in the wall-normal direction. The radial grid near the wall is generated according to reference [13,28]. The total number of grid cells is about 1 million. ...

... In a previous study, the authors of [31] found that the two-point pressure correlation length is about 3 D, indicating that the spanwise space in this study is physically reasonable. To be consistent with the study by Yu et al. [13], the velocity inlet and pressure outlet boundary conditions are prescribed. The incoming free flow velocity is 72 m/s, which is consistent with the experiment. ...

The speed increase in high-speed trains is a critical procedure in the promotion of high-speed railway technology. As an indispensable and complex structure of high-speed trains, the pantograph’s aerodynamic drag and noise is a significant limitation in the speed increase process of high-speed trains. In the present study, the hybrid method of large eddy simulation (LES) and Ffowcs Williams-Hawkings (FW-H) acoustic analogy is applied to analyze the aerodynamic and aeroacoustic performances of pantograph installed in different ways, i.e., sinking platform and fairing. The results of simulation show that the application of pantograph fairing can reduce the aerodynamic drag greatly. In addition, compared with the pantographs installed alone on the train roof, the installation of the sinking platform brings about 2 dBA reduction in sound pressure level (SPL). Meanwhile, the utilization of the pantograph fairing mainly decreases the noise in the frequency band above 1000 Hz and the largest SPL reduction is up to 3 dBA among the monitoring points. Further analysis shows that the influence of different diversion strategies on the spectral characteristics actually attenuates the dominant frequency of the panhead. In the horizontal plane, the noise directivity of the pantograph installed with a fairing is similar to the pantograph installed alone on the train roof.

... Although it is extremely difficult to eliminate the distortion completely, predicting the welding deformation can avoid such problems in the assembly process. Furthermore, welding deformation has to be tackled prior to the actual welding process to improve the quality of welded structures (Deng & Murakawa, 2007;Yu, Li, & Zhang, 2013;Yupiter et al., 2015;Zhu, Dong, Lin, Lu, & Li, 2014). ...

... The welding deformation has been examined by experimental measurements and empirical formulas over the last few decades. However, these experiences and formulas cannot accurately predict the value of the welding deformation (Yu et al., 2013). To obtain accurate results, thermal-elastic-plastic finite element method (FEM) is used along with experiments and numerical simulations. ...

... The SYSWELD can determine the residual stress and strains resulting from welding or heat treatment as well as diffusion precipitation and hydrogen diffusion. To deal with such a complex simulation in a feasible manner, SYSWELD software based on the thermo-elastic-plastic FE method, was used (Deng & Murakawa, 2007;Ueda & Yamakawa, 1971;Yu et al., 2013;Yupiter et al., 2015;Zhu et al., 2014). ...

In the automotive industry, metal inert gas (MIG) of welding technology is widely used for automotive muffler fabrication. However, the muffler is distorted by thermal deformation during the welding process. In this paper, the prediction of MIG welding-induced deformation and residual stress are simulated by SYSWELD software. The cross-section shapes of the molten pool predicted by the numerical analysis are compared to the experimental results. In the results of the stress, while compressive stresses are produced in regions away from the weld, high tensile stresses are produced in regions near the weld. Deformation values are calculated as 2.5 mm. The location of the actual welding deformation was similar to the experimental results. Based on the results, the methods to optimize the welding procedure will be provided by SYSWELD to improve muffler productivity.
Key points The prediction of MIG welding-induced deformation and residual stress are simulated by SYSWELD software. The cross-section shapes of the molten pool predicted by the numerical analysis are compared to the experimental results. The location of the actual welding deformation are similar to the experimental results. Based on the results, the methods will be provided by SYSWELD to improve muffler productivity.

... Current research on the aerodynamic noise of the pantograph mainly focuses on the location and classification of noise sources [Thompson, Latorre Iglesias, Liu et al. (2015); Mellet, Létourneaux, Poisson et al. (2006); Nagakura (2006)], low-noise design based on the main aerodynamic noise sources of the components [Ikeda, Suzuki and Yoshida (2006); Sueki, Ikeda and Takaishi (2009)], and the semi-empirical models that are currently also used in the industry to predict aerodynamic noise from pantographs [Latorre Iglesias, Thompson and Smith (2017)]. However, scholars have analysed the aerodynamic noise characteristics of the pantograph without crosswind conditions [Liu, Hu, Thompson et al. (2018); Yu, Li and Zhang (2013); ; Tan, Yang, Tan et al. (2018); Zhang, Zhang, Li et al. (2017); ]. Quantitative studies of the aerodynamic noise behaviours and aeroacoustic characteristics of the pantograph under crosswind are rare. ...

... The first, second and third terms on the right side of Eq. (1) represent the monopole sources, dipole sources and quadrupole sources, respectively. Because low Mach number flow is simulated for the pantograph under crosswind, the quadrupole sources from the Lighthill stress tensor may be neglected ; Yu, Li and Zhang (2013)]. Also, the monopole sources do not need to be considered because the pantograph surface can be seen as arbitrary rigid bodies and without moving in the fluid field, and the pulsating volume quantity becomes zero ], that is ...

... On the cylindrical wave, the attenuation level of the SPL is approximately 3 dBA. These observations indicate that the acoustic attenuation characteristics of the pantograph under crosswind are analogous to the inflow transit a regular circular cylinder, which is a typical point source of radiated noise on a spherical wave [Yu, Li and Zhang (2013); Zhang, Zhang and Li (2017)]. ...

... Sound analogy theory is the dominant theoretical basis for the current research on the aerodynamic noise generation mechanism of high-speed trains. Dipole noise sources are generally considered to be the dominant noise source [16] for high-speed trains and can be described by the fluctuating pressure [17] on the train surface. The fluctuating pressure on the train surface is closely related to the structure of the flow field and the induced mechanism of the flow field structure in the different areas for the high-speed train. ...

... For the intercoach windshield area, the cavity vocalization is its dominant vocal mechanism [23,24]. For the pantograph area, the airflow separation and the vortex shedding from the rod and their interactions are the dominant reasons for the flow field structure in this area [17,25,26]. For the bogie area, the flow pattern of the cavity and the bluff body flow pattern such as the wheelset and axle are combined in the narrow space of the bogie cavity, which is the dominant inducing mechanism of the complex flow field structure in this area [27,28]. ...

... Characteristics. The mean square root of the rate of fluctuating pressure (dpdt-rms) on the high-speed train is defined by (17) and characterizes the average effect of the sound source intensity in the sampling time. Its distribution cloud is shown in Figure 12. ...

We aim to study the characteristics and mechanism of the aerodynamic noise sources for a high-speed train in a tunnel at the speeds of 50 m/s, 70 m/s, 83 m/s, and 97 m/s by means of the numerical wind tunnel model and the nonreflective boundary condition. First, the large eddy simulation model was used to simulate the fluctuating flow field around a 1/8 scale model of a high-speed train that consists of three connected vehicles with bogies in the tunnel. Next, the spectral characteristics of the aerodynamic noise source for the high-speed train were obtained by performing a Fourier transform on the fluctuating pressure. Finally, the mechanism of the aerodynamic noise was studied using the sound theory of cavity flow and the flow field structure. The results show that the spectrum pattern of the sound source energy presented broadband and multipeak characteristics for the high-speed train. The dominant distribution frequency range is from 100 Hz to 4 kHz for the high-speed train, accounting for approximately 95.1% of the total sound source energy. The peak frequencies are 400 Hz and 800 Hz. The sound source energy at 400 Hz and 800 Hz is primarily from the bogie cavities. The spectrum pattern of the sound source energy has frequency similarity for the bottom structure of the streamlined part of the head vehicle. The induced mode of the sound source energy is probably the dynamic oscillation mode of the cavity and the resonant oscillation mode of the cavity for the under-car structure at 400 Hz and 800 Hz, respectively. The numerical computation model was checked by the wind tunnel test results.

... Many studies have been carried out to identify pantograph noise sources [8][9][10] and to attempt to reduce its noise [11][12][13][14][15][16][17][18]. By comparison, the generation of aerodynamic noise from the pantograph recess, representing a rectangular cavity, and its flow interacting with pantograph components are less well understood even though the noise from the pantograph recess may have a similar level to that from the pantograph [7]. ...

... L p ∼ 60log 10 N, which is typical of dipole sound [69]. Yu et al. [10] predicted the aerodynamic noise emission of a pantograph system at 350 km/h using a hybrid method of non-linear acoustic solver (NLAS) and FW-H. They found that the main mechanism is the periodic vortex shedding, which generates Aeolian tones [3] around the pantograph structures, especially the panhead. ...

... As a result of the optimisation, they achieved a 2 dB reduction of noise compared with the original conventional insulation plates. Yu et al. [10] modelled numerically various types of pantograph insulation cover, as shown in Figure 2.11. It was found that one case, which covered the sides of the pantograph (see Figure 2.11(a)), reduced the tonal noise by 3 dB, whereas all the other cases (See Figure 2.11(b), (c), (d)) performed poorly and produced more noise than the case without the cover. ...

As high speeds bring higher levels of noise, noise reduction has become an important consideration for high-speed train design. In this study, the flow behaviour of a simplified geometry representing a high-speed train roof and cavity with pantographs at 1/10 scale is investigated. Computational Fluid Dynamics simulations are used based on the Improved Delayed Detached-Eddy simulation method to determine the near-field flow behaviours. The equivalent source terms are then used to predict the far-field acoustic pressure using the Ffowcs Williams-Hawkings acoustic analogy.
The effect of the pantograph cavity is studied by comparing the flow behaviour and radiated noise from cases with two pantographs, one raised and one retracted, mounted either in a cavity or on a flat surface. In comparison with case with the flat surface, the flow around the pantographs with the cavity has slightly different characteristics. The cavity slightly reduces the flow velocity upstream of the raised pantograph, and changes the unsteady flow and its interactions with the pantographs, which leads to reduced surface pressure fluctuations and noise radiated from the raised pantograph. The trailing edge of the cavity also generates a highly unsteady flow.
The highly unsteady flow over the cavity is significantly reduced by introducing modified leading and trailing cavity edges, which are rounded or angled. Consequently, noise radiated from the cavity is reduced compared to a rectangular cavity. Furthermore, the effect of rounded cavity edges on the flow over the pantographs is also investigated by comparing the flow features and noise contributions from the cases without rounded cavity edges. A slightly lower flow speed occurs around the upper parts of the raised pantograph, whereas the flow velocity in the cavity is slightly increased compared to the rectangular cavity. It is shown that, by rounding the cavity edges, a reduction in radiated noise can be obtained.
The influence of three different roof configurations is also studied by comparing the flow behaviour, including flow separations, reattachment and vortex shedding, which are potential noise sources. A highly unsteady flow occurs downstream when the train roof has a cavity or ramped cavity due to flow separation at the cavity trailing edge, while vortical flow is generated by the side insulation plates. When the retracted pantograph is located inside the ramped cavity, its noise contribution is less important. Furthermore, the insulation plates also generate tonal components in the noise spectra. For the three configurations considered, the roof configuration with a conventional cavity radiates the least A-weighted noise at the side receiver.

... Tan and Xie [12] used LES, the scale adaptive simulation(SAS), the improved delayed detached eddy simulation with shear-stress transport k-ω (IDDES SST k-ω), the delayed detached eddy simulation with shear-stress transport k-ω (DDES SST k-ω), and the delayed detached eddy simulation with realizable k-ε(DDES Realizable k-ε) models to investigate the flow-field structures, the aeroacoustic sources, and the aeroacoustics of pantographs. By means of a hybrid method of NLAS and FW-H acoustic analogy, Yu et al. [13] studied the aerodynamic noise of the pantograph system, specifically to predict the influence of the pantograph covers on noise in the speed range. Besides the methods used to conduct acoustic propagation as mentioned above, there are still other methods for universal acoustic propagation calculations such as the acoustic boundary element method (BEM) and the acoustic finite element method (FEM). ...

... To predict the OASPL in the region from the pantograph to the far field, it is found that the logarithm function, OASPL = OASPL0 -b ln(x + c), is fitted appropriately using the values of the OASPL under the relation between the OASPL and the distance in the range of 0 ≤ y ≤ 30 m. Besides, under the same configuration base, the OASPL obtained by the down-pantograph is higher than that by the up-pantograph. To evaluate the OASPL caused by the pantograph in the far-field region, it is acceptable if the distance from the sound source is more than 25 m, the sound source is assumed as a point source [13]. Therefore, the sound pressure propagation can be considered as the spherical surface from the point source center and the attenuation value ∆L of the OASPL from the point source in the far-field regions is computed by the equation: ∆L = 20log(r/r0). ...

... To predict the OASPL in the region from the pantograph to the far field, it is found that the logarithm function, OASPL = OASPL 0 − b × ln(x Besides, under the same configuration base, the OASPL obtained by the down-pantograph is higher than that by the up-pantograph. To evaluate the OASPL caused by the pantograph in the far-field region, it is acceptable if the distance from the sound source is more than 25 m, the sound source is assumed as a point source [13]. Therefore, the sound pressure propagation can be considered as the spherical surface from the point source center and the attenuation value ∆L of the OASPL from the point source in the far-field regions is computed by the equation: ∆L = 20log(r/r0). ...

The high-speed-train pantograph is a complex structure that consists of different rod-shaped and rectangular surfaces. Flow phenomena around the pantograph are complicated and can cause a large proportion of aerodynamic noise, which is one of the main aerodynamic noise sources of a high-speed train. Therefore, better understanding of aerodynamic noise characteristics is needed. In this study, the large eddy simulation (LES) coupled with the acoustic finite element method (FEM) is applied to analyze aerodynamic noise characteristics of a high-speed train with a pantograph installed on different configurations of the roof base, i.e. flush and sunken surfaces. Numerical results are presented in terms of acoustic pressure spectra and distributions of aerodynamic noise in near-field and far-field regions under up- and down-pantograph as well as flushed and sunken pantograph base conditions. The results show that the pantograph with the sunken base configuration provides better aerodynamic noise performances when compared to that with the flush base configuration. The noise induced by the down-pantograph is higher than that by the up-pantograph under the same condition under the pantograph shape and opening direction selected in this paper. The results also indicate that, in general, the directivity of the noise induced by the down-pantograph with sunken base configuration is slighter than that with the flush configuration. However, for the up-pantograph, the directivity is close to each other in Y-Z or X-Z plane whether it is under flush or sunken roof base condition. However, the sunken installation is still conducive to the noise environment on both sides of the track.

... More comprehensive flow field information can be obtained through numerical simulation, which can help people understand the mechanism of aerodynamic noise more deeply. In the aspect of numerical simulation, Yu et al. [10] applied the non-linear acoustic solver (NLAS) combined with FW-H equation to analyze the aerodynamic noise characteristics of a simplified DSA-350 pantograph and the noise reduction effects of four different designs of pantograph fairing. They found that the aerodynamic drag of pantograph area would be increased by all four schemes, and only the scheme using side sound insulation panels could reduce the noise of pantograph. ...

... According to the solution setup mentioned above, the aerodynamic noise generated by a cylinder with a diameter of 10 mm at inflow velocity of 72 m/s is simulated. This case is also used to verify the calculation method in other literatures on pantograph aerodynamic noise research [10,19,25]. Fig. 4 shows the calculation conditions and the computational mesh. ...

... Lee and Cho [11], Ikeda et al. [12], and Kurita [13] developed an optimized pantograph structure and tested the proposed PS207 pantograph in a noise reduction experiment, in which the noise reduction effects of a low-noise panhead structure in combination with the new pantograph type were studied in wind tunnel tests. Yu et al. [14] also considered the effect of a pantograph fairing installed on the roof of a train. They found that if the fairing consisted of two sideward baffles acting as noise barriers, then a noise reduction of 3 dB could be achieved. ...

... , can be used to evaluate the noise distribution along the train surface [14,35]. ...

A broadband noise source model based on Lighthill's acoustic theory was used to perform numerical simulations of the aerodynamic noise sources for a high-speed train. The near-field unsteady flow around a high-speed train was analysed based on a delayed detached-eddy simulation (DDES) using the finite volume method with high-order difference schemes. The far-field aerodynamic noise from a high-speed train was predicted using a computational fluid dynamics (CFD)/Ffowcs Williams-Hawkings (FW-H) acoustic analogy. An analysis of noise reduction methods based on the main noise sources was performed. An aerodynamic noise model for a full-scale high-speed train, including three coaches with six bogies, two inter-coach spacings, two windscreen wipers, and two pantographs, was established. Several low-noise design improvements for the high-speed train were identified, based primarily on the main noise sources; these improvements included the choice of the knuckle-downstream or knuckle-upstream pantograph orientation as well as different pantograph fairing structures, pantograph fairing installation positions, pantograph lifting configurations, inter-coach spacings, and bogie skirt boards. Based on the analysis, we designed a low-noise structure for a full-scale high-speed train with an average sound pressure level (SPL) 3.2 dB(A) lower than that of the original train. Thus, the noise reduction design goal was achieved. In addition, the accuracy of the aerodynamic noise calculation method was demonstrated via experimental wind tunnel tests.

... The aerodynamic noise of a fullscale DSA350 pantograph at 350 km/h was investigated numerically by Yu et al. [83], using a hybrid method with FW-H acoustic analogy. They showed that the aerodynamic noise from the pantograph was generated by the flow separation, the unsteady wake and the strong interaction between components. ...

... Yu et al. [83] also considered the effect of a pantograph cover installed on the train roof numerically. They found that if the cover consists of only two sideward baffles it can reduce the noise by 3 dB by acting as a noise barrier. ...

At speeds above 300-350 km/h, the main source of noise from trains is the aerodynamic noise caused by the air flow over the train structure. The sound level increases with train speed at a rate of between 60 and 80 times the logarithm of the speed so that, as speeds increase further, the noise increases dramatically. The main aerodynamic noise is produced by the air flow passing over the pantograph, the train nose, the bogie region and cavities such as the pantograph recess and the inter-coach gap. Experimental and numerical methods for studying aerodynamic noise are reviewed including the use of microphone arrays, wind tunnels, computational fluid dynamics and semi-empirical methods. Potential mitigation measures that can control aerodynamic noise are also reviewed.

... They measured experimentally the noise radiated by different tapered cylinders connected by the knee region and used CFD analysis (κ − turbulence model) in order to investigate the flow behaviour around the knee models. Other examples are found in the application by Yu et al. [15] of a hybrid method of Non-Linear Acoustic Solver (NLAS) and Ffowcs Williams-Hawkings (FW-H) acoustic analogy to predict the aerodynamic noise produced by a simplified pantograph type DSA350 for an incident flow speed of 350 km/h, and in the numerical methods applied by Lei et al. [16] to predict the noise radiated by the pantograph struts, dividing the calculation into an unsteady incompressible flow analysis using the Finite Element Method (FEM) and an acoustic analysis using the Boundary Element Method (BEM). ...

At typical speeds of modern high-speed trains the aerodynamic noise produced by the airflow over the pantograph is a significant source of noise. Although numerical models can be used to predict this they are still very computationally intensive. A semi-empirical component-based prediction model is proposed to predict the aerodynamic noise from train pantographs. The pantograph is approximated as an assembly of cylinders and bars with particular cross-sections. An empirical database is used to obtain the coefficients of the model to account for various factors: incident flow speed, diameter, cross-sectional shape, yaw angle, rounded edges, length-to-width ratio, incoming turbulence and directivity. The overall noise from the pantograph is obtained as the incoherent sum of the predicted noise from the different pantograph struts. The model is validated using available wind tunnel noise measurements of two full-size pantographs. The results show the potential of the semi-empirical model to be used as a rapid tool to predict aerodynamic noise from train pantographs.

... Results showed that beams at the top of pantograph were main sources of aerodynamic noises. Yu [17] adopted nonlinear acoustic solver and acoustic analogy theory to carry out numerical research on 3 kinds of pantograph air deflectors and found their sound pressure level decreased by 3 dB in the case of designing the air deflector structure of pantograph similar to windshield in a span-wise direction. Huang [18] established an analytical model for the aerodynamic noise of bogies, focused on studying aerodynamic noises when bogies were noise sources, and analyzed the noise reduction effect of bogies on both sides of radiation noises in the case of applying the apron board of bogies. ...

This paper established a computational model for the aerodynamic noise of a high-speed train with 3-train formation including 3 bodies, 6 bogies, 2 windshields and 1 pantograph system. Based on Lighthill acoustic theory, this paper adopted large eddy simulation (LES) and FW-H model to conduct numerical simulation for the aerodynamic noise of high-speed trains and analyzed the distribution of aerodynamic flow behavior and noises of the whole train. Researched results showed that the main aerodynamic noise sources of high-speed trains were in pantograph, pantograph region, streamlined region of head train, bogies, bogie region, windshield region, air conditioning and other regions. Pantograph head, junction of upper arm and lower arm, and chassis region were main aerodynamic noise sources of pantograph. Compared with other 5 bogies, bogie at the first end of head train was main aerodynamic noise source. In addition, vortex shedding and fluid separation were main reasons for the aerodynamic noise of high-speed trains. When the high-speed train ran at the speed of 300 km/h and 400 km/h, the main energy of the whole train focused on the range of 1000 Hz-4000 Hz. Aerodynamic noises were broadband noises in the analyzed frequency domain. At the longitudinal observation point which was 25 m away from the center line of track and 25 m away from the nose tip of head train, the total noise sound pressure level reached up to maximum values 96.5 dBA and 101.4 dBA, respectively. Compared with inflow, wake flow had a greater influence on the aerodynamic noise around high-speed trains. The main radiation direction of pantograph aerodynamic noises was the left and right sides of pantograph head. In addition, the main radiation energy of pantograph aerodynamic noises was in mid-high frequency. In the part of high frequency, pantograph head made the greatest contribution to aerodynamic noises in the far field.

... [4-5] * (2013BAG24B02) (2016YFB1200403) (U1234208) 20160323 20161129 [1,[6][7] KING III [8] NOGER [9] SUEKI [10] E2-1000 PS207 360 km/h 1.9 dBA LEE [11][12][13] PS207 YU [14] 3 DSA350 3 dB [15] 1 kHz 100 700 Hz 20 Hz 5 kHz 30 dB [16] ZHANG [17] 3. [19] CFD [20] FLUENT 5 kHz ∆t=1/(2×f max )=1.0×10 −4 s ∆f≤2 Hz N step≥ 1/(∆f× ∆t)=5 000 3 000 5 000 [17,23] (1) 371-414. ...

Based on Lighthill acoustic theory in this paper, broadband noise source model, large eddy simulation and Ffowcs Williams-Hawkings equation are used to perform numerical simulations in aerodynamic noise of a high-speed train. The aerodynamic noise model of full scale high-speed train is established. The main aerodynamic noise source and the characteristics of far-field aerodynamic noise of a high-speed train are analyzed, as well the analysis methods of noise reduction based on the main noise source is presented. The low-noise design and improvement of high-speed train primarily based on the main noise source such as the knuckle-downstream direction/the knuckle-upstream direction, the different pantograph fairings and the different installations of pantograph fairings. Based on the above analysis, the low-noise structure of full scale high-speed train pantograph which max sound pressure level is 3.1 dBA lower than the original trains is obtained. Thus the designed goal of noise reduction has been achieved. In addition, the accuracy and effectiveness of calculating method of aerodynamic noise has been proved by wind tunnel test.

... In addition, the long axis of the oval should be consistent with the flow direction of airflow. Yu [21] designed 4 kinds of air deflectors and numerically simulated pantographs to find that the noise reduction effect was obvious and sound pressure level decreased by about 3dB after an air deflector was adopted. King [22] adopted dipole source to describe the aerodynamic noise caused by the vortex shedding of pantographs and found that the far-field aerodynamic noise of pantographs was approximately linear to the logarithm of train speed. ...

The aerodynamic noise of high-speed trains not only causes interior noise pollution and reduces the comfort of passengers, but also seriously affects the normal life of residents. With the increase of running speed of trains, aerodynamic noises will be more than wheel-rail noises and become the main noise source of high-speed trains. This paper established a computational model for the aerodynamic noise of a CRH2 high-speed train with 3-train formation including 3 train bodies and 6 bogies, adopted the detached eddy simulation (DES) to conduct numerical simulation for the flow field around the high-speed train, applied Ffowcs Williams-Hawkings acoustic model to conduct unsteady computation for the aerodynamic noise of high-speed trains, and analyzed the far-field aerodynamic noise characteristics of high-speed trains. Studied results showed: The main energy of the complete train was mainly within the range of 613 Hz-2500 Hz when the high-speed train ran at the speed of 350 km/h. In the whole frequency domain, it was a broadband noise. Regarding the longitudinal observation point which was 25 m away from the center line of track and 6m away from the nose tip of head train, the sound pressure level of total noises reached the maximum value 88.9 dBA. The maximum sound pressure level of the noise observation point which was 7.5 m away from the center line of track was around the first bogie of head train. Various components made different contributions to the aerodynamic noise of the complete train, and the order was head train, mid train, bogie system (6 bogies) and tail train. The first bogie of head train made the greatest contribution to bogie system and was the main aerodynamic noise source of the complete train.

... (i) The irregular structure of the pantograph bogie and coupling component of the train is the main generating region of aerodynamic noise [66][67][68][69]; ...

High-speed railway aerodynamics is the key basic science for solving the bottleneck problem of high-speed railway development. This paper systematically summarizes the aerodynamic research relating to China’s high-speed railway network. Seven key research advances are comprehensively discussed, including train aerodynamic drag-reduction technology, train aerodynamic noise-reduction technology, train ventilation technology, train crossing aerodynamics, train/tunnel aerodynamics, train/climate environment aerodynamics, and train/human body aerodynamics. Seven types of railway aerodynamic test platform built by Central South University are introduced. Five major systems for a high-speed railway network—the aerodynamics theoretical system, the aerodynamic shape (train, tunnel, and so on) design system, the aerodynamics evaluation system, the 3D protection system for operational safety of the high-speed railway network, and the high-speed railway aerodynamic test/computation/analysis platform system—are also introduced. Finally, eight future development directions for the field of railway aerodynamics are proposed. For over 30 years, railway aerodynamics has been an important supporting element in the development of China’s high-speed railway network, which has also promoted the development of high-speed railway aerodynamics throughout the world.

... 受电弓受到的抬升力与列车运行速度的平方近似呈 线性关系 [6] 。研究表明，高速列车受电弓系统产生 的气动噪声明显大于其他部位，是主要的噪声 源 [7][8][9] 。 针对高速列车受电弓的气动特性，国内外学者 做了大量的研究工作。POMBO 等 [10] 采用试验和数 值模拟相结合的方法对横风下气动力对弓网系统的 影响进行了研究；VISCARDI 等 [11] 采用分析和数值 模拟的方法研究了高速列车受电弓的气动噪声； LEE 等 [12] 对不同臂杆形式的受电弓进行了风洞试 验研究，对矩形弓头和流线型弓头受电弓的气动性 能进行了分析比较。在国内，张建辉等 [13] 采用风洞 试验的方法研究了受电弓导流罩和风挡对受电弓气 动阻力的影响；郭迪龙等 [14] 采用脱体涡模拟方法对 有无横风条件下高速列车受电弓的非定常气动特性 进行了研究；李瑞平等 [15] 对开口和闭口运行时高速 受电弓的气动力进行数值模拟，仿真结果与试验结 果基本一致；付善强等 [16] 对横风作用下高速受电弓 弓头升力、整弓气动力以及风致振动特性进行了风 洞试验研究；ZHANG 等 [17] 采用数值模拟方法对受 电弓安装位置对高速列车气动性能的影响进行了研 究。受电弓系统的外形复杂，其后部气流受到强烈 的激扰，具有明显的非定常气动特性。受电弓部位 的气动噪声主要是由其周围的非定常流场结构引起 的，同时导致受电弓受到的气动力也呈现明显的震 荡特性，从而影响受电弓的气动性能。目前，对受 电弓气动特性的研究多局限于受电弓本身，没有考 虑列车车体对受电弓周围流场的影响。气流流经列 车时沿着列车纵向向后边界层厚度逐渐增大， 受电弓 安装位置对受电弓的气动特性有着重要影响 [17][18] 。 因 此，研究不同位置受电弓的非定常气动特性具有重 要的意义。 分离涡模拟 (Detached eddy simulation，DES) 方 法 兼 具 雷 诺 平 均 方 法 (Reynolds average Navier-Stokes ， RANS) 和 大 涡 模 拟 (Large eddy simulation，LES)的优点，近年来被用于列车周围瞬 态流场的模拟， 计算结果与试验结果吻合较好 [19][20] 。 因此， 本文采用 DES 方法对高速列车周围流场进行 数值计算，并对不同位置受电弓受到气动力的非定 常特性及受电弓周围流场结构进行详细分析。 1 高速列车空气动力学模型 ...

To study the unsteady aerodynamic characteristics of pantographs in different positions of high-speed trains, the aerodynamic models of high-speed trains are established based on the theory of computational fluid dynamics. A train with eight coaches is adopted as the train model, which includes a head coach, six middle coaches and a tail coach. The pantograph model has two pantographs, which includes a lifted pantograph and a folded pantograph. The pantographs are fixed on the front end or the rear end of the first middle car, or fixed on the front end or the rear end of the sixth middle car. The flow fields around high-speed trains running in the open air without crosswinds are numerically simulated by the detached eddy simulation (DES) method. The train running speed is 350 km/h. The characteristics of the unsteady aerodynamic forces acting on the pantographs fixed in different positions of high-speed trains are presented from the numerical results, which include the characteristics of the time domain, the frequency domain, and the unsteady flow structures around the pantographs. The results show that the time-average values of the aerodynamic drag force and lift force of the pantographs tend to decrease as the fixing position of pantographs moves backward along the longitudinal direction of the high-speed train. When the lifted pantograph is in the knuckle-downstream direction, the time-average values of the aerodynamic lift forces of the pantographs are smaller than those with the lifted pantograph in the knuckle-upstream direction, and the amplitudes in the aerodynamic lift force and side force of the sliding plate of the lifted pantograph are also smaller than those with the lifted pantograph in the knuckle-upstream direction. The fluctuations of the lift force and side force of the sliding plate of the lifted pantograph have broad frequency distributions, and their main frequencies range from 0 Hz to 300 Hz.

... In the meanwhile, the disturbance effect of pantographs on airflows will cause a large aerodynamic noise when a high-speed train runs at a high speed. Therefore, the aerodynamic characteristics and noises of pantographs have been the studied hotspot of science researchers due to the requirements for safety and comfort [1][2][3][4][5][6]. Li [7] established a three-dimensional geometric model of pantographs, simulated the flow field around pantographs based on the computational fluid dynamics and finite volume method and also built a computational model for the aerodynamic noise of pantographs. ...

Pantographs are an important part of power supply systems of high-speed trains, whose good working performance is a guarantee for the steady power supply and safety operation of high-speed trains. The aerodynamic drag of pantographs will have negative impacts on the running of high-speed trains. In the meanwhile, the disturbance effect of pantographs on airflow will cause large aerodynamic noises when a high-speed train runs at a high speed. Therefore, this paper conducted a numerical simulation for the flow field and aerodynamic noises of pantographs on the symmetrical plane, compared simulation results with experimental one, verified the correctness of the numerical simulation model, and further studied the impact of pantograph angles on radiation noises. When pantographs were working, cylindrical rods which were vertical to the direction of airflows had a more obvious disturbance effect on airflows and caused a larger range of vortex shedding. Shedding vortexes were mainly distributed at the pantograph head, hinge joints between upper and lower arms, and rear bases. Near-field aerodynamic noises on the longitudinal symmetrical plane of pantographs were distributed at the lower arm, middle hinge joints and bases. The maximum appeared at the middle hinge joints. The intensity of vortexes at the middle hinge joints, lower arms and bases when the pantograph angle was 60° was more than that at other pantograph angles. In this case, the near-field aerodynamic noise of pantographs was more than that of other pantograph angles. In addition, radiation noises of observation points of pantographs in all directions presented an obvious linear relationship. The far-field radiation noise of pantographs was gradually decreased with the increased distance from pantographs. In addition, the far-field radiation noises of pantographs on the same vertical plane had the intensity with the same level.

... They found that insulators with elliptic cross sections whose long axis consists with the airflow direction are optimal. Yu et al. [16] designed three kinds of pantograph guide guards and conducted a noise reduction analysis based on opened running mode of pantographs, finding that noise reduction effects were obvious and sound pressure levels were decreased by 3 dB adopting this pantograph guide guard similar to air barriers. ...

Pantographs are important devices on high-speed trains. When a train runs at a high speed, concave and convex parts of the train cause serious airflow disturbances and result in flow separation, eddy shedding, and breakdown. A strong fluctuation pressure field will be caused and transformed into aerodynamic noises. When high-speed trains reach 300 km/h, aerodynamic noises become the main noise source. Aerodynamic noises of pantographs occupy a large proportion in far-field aerodynamic noises of the whole train. Therefore, the problem of aerodynamic noises for pantographs is outstanding among many aerodynamics problems. This paper applies Detached Eddy Simulation (DES) to conducting numerical simulations of flow fields around pantographs of high-speed trains which run in the open air. Time-domain characteristics, frequency-domain characteristics, and unsteady flow fields of aerodynamic noises for pantographs are obtained. The acoustic boundary element method is used to study noise radiation characteristics of pantographs. Results indicate that eddies with different rotation directions and different scales are in regions such as pantograph heads, hinge joints, bottom frames, and insulators, while larger eddies are on pantograph heads and bottom frames. These eddies affect fluctuation pressures of pantographs to form aerodynamic noise sources. Slide plates, pantograph heads, balance rods, insulators, bottom frames, and push rods are the main aerodynamic noise source of pantographs. Radiated energies of pantographs are mainly in mid-frequency and high-frequency bands. In high-frequency bands, the far-field aerodynamic noise of pantographs is mainly contributed by the pantograph head. Single-frequency noises are in the far-field aerodynamic noise of pantographs, where main frequencies are 293 Hz, 586 Hz, 880 Hz, and 1173 Hz. The farther the observed point is from the noise source, the faster the sound pressure attenuation will be. When the distance of two adjacent observed points is increased by double, the attenuation amplitude of sound pressure levels for pantographs is around 6.6 dB.

... Noise reduction effects of the low-noise pantograph head shape and novel pantograph were verified in the wind tunnel experiment. Yu et al. [16] designed 3 fairing structures and carried out numerical simulation analysis of the pantograph, finding that noise reduction effects were obvious and the sound pressure level decreased by about 3 dB after the application of the fairing similar to a windshield structure. Liu et al. [17] adopted a hybrid computation method in which LIU used large eddy simulation to obtain the equivalent aerodynamic noise source of flow fields and then applied it on boundary elements of sound fields, so as to make detailed research of dipole noise source characteristics on the pantograph surface. ...

Ground transportation means and aircrafts with high-speed running are composed of many rod components. Aerodynamic noise generated therefrom is very outstanding. Reduction of the aerodynamic noise of rods becomes a hot topic in recent years. Most reported studies are tentative researches on aerodynamic noise of a pantograph or involve noise reduction of the pantograph with using porous materials or reshaping rod surfaces. Through using porous materials and reshaping rod surface, the aerodynamic noise of pantograph can be reduced to a certain extent, but the aerodynamic resistance will be increased and it is not convenient for practical application in engineering. Regarding this situation, the paper explores noise reduction performance of a feather on the back of a carrier pigeon and conducts the bionic design on rod surface. Through numerical simulation, the paper researches noise reduction performance of the bionic structure on the rod surface, reveals the mechanism of bionic noise reduction, and explores noise reduction effects of bionic structural rods on pantographs of the high-speed trains.

... 36 This method has gained growing attention in recent years for the flow-induced noise prediction. [37][38][39] For high-speed train-related issues, Zhu et al. 40 and Yu et al. 41 used the FW-H acoustic analogy to study the noise produced by a 1/10th scale isolated simplified wheelset model and isolated pantograph system. From their study, the SPL, OASPL, A-weighted SPL as well as noise directivity were analysed for the individual components of train. ...

The flow field and sound propagation around a three-coach 1/8th scale high-speed passenger train were obtained using a detached-eddy simulation and the Ffowcs-Williams and Hawkings acoustic analogy. The Reynolds number of flow based on the train height and speed was 2,000,000. The numerical results of the flow and aeroacoustic fields were validated using wind tunnel experiments and full-scale data, respectively. Features of overall sound pressure level, sound pressure level and A-weighted sound pressure level of typical measuring points are discussed. The sound propagated by a high-speed train is shown as a broadband noise spectrum including tonal component, where high sound pressure levels are concentrated on the low-frequency range from 10 Hz to 300 Hz. The inter-carriage gap is found to cause distinct tonal noise in contrast to the other parts of the train that cause a broadband noise. The negative log law has been used to study the influence of distance from the centre of track on the sound pressure level, where a good fit is shown at low-frequency ranges. The peak values of A-weighted sound pressure level from both full-scale experiment and simulation results occur at approximately 1 kHz, where simulation results show almost the same range as the experiment. The surface of each component of the train as well as the whole train are chosen as the integral surface for the Ffowcs-Williams and Hawkings computation of the far-field noise characteristics. It was found that the sound source generated by a high-speed train is mainly dipole, and the largest noise was obtained from the leading bogie. The results of this paper provide, for the first time, a better understanding of the aeroacoustic field around a three-coach train model, and the paper has the potential to assist engineers to design high-speed trains with aeroacoustic noise reduction in a better manner.

... A pair of baffles with half of the height of the pantograph on both sides can lessen noise by about 3 dB [23] Noise contribution from high-speed train roof configuration of cavities, ramped cavities, flat roofs ...

Since the invention of the train, the problem of train noise has been a constraint on the development of trains. With increases in train speed, the main noise from high-speed trains has changed from rolling noise to aerodynamic noise, and the noise level and noise frequency range have also changed significantly. This paper provides a comprehensive overview of recent advances in the development of high-speed train noise. Firstly, the train noise composition is summarized; next, the main research methods for train noise, which include real high-speed train noise tests, wind tunnel tests, and numerical simulations, are reviewed and discussed. We also discuss the current methods of noise reduction for trains and summarize the progress in current research and the limitations of train body panels and railroad sound barrier technology. Finally, the article introduces the development and potential future applications of acoustic metamaterials and proposes application scenarios of acoustic metamaterials for the specific needs of railroad sound barriers and train car bodies. This synopsis provides a useful platform for researchers and engineers to cope with problems of future high-speed rail noise in the future.

... Many important factors such as the elastic deformations of tracks and inter-vehicle interaction were ignored. For a better understanding of train derailment mechanism and dynamic derailment behavior, the existing models need to be further improved in the space scale of modeling trains coupled with tracks and the flexible modelling of their key components [27][28][29]. This paper presents a three-dimensional (3D) dynamic model of a highspeed train coupled with a flexible nonlinear track to carry out dynamic derailment analysis. ...

The running safety of high-speed trains has become a major concern of the current railway research with the rapid development of high-speed railways around the world. The basic safety requirement is to prevent the derailment. The root causes of the dynamic derailment of high-speed trains operating in severe environments are not easy to identify using the field tests or laboratory experiments. Numerical simulation using an advanced train–track interaction model is a highly efficient and low-cost approach to investigate the dynamic derailment behavior and mechanism of high-speed trains. This paper presents a three-dimensional dynamic model of a high-speed train coupled with a ballast track for dynamic derailment analysis. The model considers a train composed of multiple vehicles and the nonlinear inter-vehicle connections. The ballast track model consists of rails, fastenings, sleepers, ballasts, and roadbed, which are modeled by Euler beams, nonlinear spring-damper elements , equivalent ballast bodies, and continuous viscoelastic elements, in which the modal superposition method was used to reduce the order of the partial differential equations of Euler beams. The commonly used derailment safety assessment criteria around the world are embedded in the simulation model. The train–track model was then used to investigate the dynamic derailment responses of a high-speed train passing over a buckled track, in which the derailment mechanism and train running posture during the dynamic derailment process were analyzed in detail. The effects of train and track modelling on dynamic derailment analysis were also discussed. The numerical results indicate that the train and track modelling options have a significant effect on the dynamic derailment analysis. The inter-vehicle impacts and the track flexibility and nonlinearity should be considered in the dynamic derailment simulations.

... The airflow separation, vortex shedding and interaction around the rods are the main causes of aerodynamic noise induced by the pantograph. The vortex shedding generates periodic forces on the rods, forming a strong dipole sound source, and making aerodynamic noise, with the vortex shedding frequency as the peak frequency [17][18][19][20]. Besides, an annular cavity exists around the windshield. ...

... Recently, several studies [2][3][4][5][6] were carried out on the aerodynamic noise of high-speed trains. Various methods such as full-scale measurements, scaled-model tests in a wind tunnel, and numerical approaches were used, and the common results were that the first bogie, the first pantograph, and the first intercoach spacing were the aerodynamic sources contributing most to the radiated noise field. ...

The high-speed train interior noise induced by the exterior flow field is one of the critical issues for product developers to consider during design. The reliable numerical prediction of noise in a passenger cabin due to exterior flow requires the decomposition of surface pressure fluctuations into the hydrodynamic (incompressible) and the acoustic (compressible) components, as well as the accurate computation of the near aeroacoustic field, since the transmission characteristics of incompressible and compressible pressure waves through the wall panel of the cabin are quite different from each other. In this paper, a systematic numerical methodology is presented to obtain separate incompressible and compressible surface pressure fields in the wavenumber–frequency and space–time domains. First, large eddy simulation techniques were employed to predict the exterior flow field, including a highly-resolved acoustic near-field, around a high-speed train running at the speed of 300 km/h in an open field. Pressure fluctuations on the train surface were then decomposed into incompressible and compressible fluctuations using the wavenumber–frequency analysis. Finally, the separated incompressible and compressible surface pressure fields were obtained from the inverse Fourier transform of the wavenumber–frequency spectrum. The current method was illustratively applied to the high-speed train HEMU-430X running at a speed of 300 km/h in an open field. The results showed that the separate incompressible and compressible surface pressure fields in the time–space domain could be obtained together with the associated aerodynamic source mechanism. The power levels due to each pressure field were also estimated, and these can be directly used for interior noise prediction.

... Many approaches have been used to investigate the aerodynamic noise characteristics for the pantograph of high-speed trains. However, Ffowcs Williams-Hawkings (FW-H) equation [43] was widely used to simulate the flow field and the noise radiated from the farfield of the pantograph components [31,[44][45][46]. In the present investigation, the aeroacoustics noise generated from the pantograph is then predicted by using the FW-H approach. ...

This article aims to investigate the aerodynamic noise of the pantograph of the high-speed trains in different operating conditions. CFD technique was used to assess the acoustic noise of the pantograph components. Three-dimensional computational simulations were performed using FLUENT software. Comprehensive analyses of the acoustic pressure and the air velocity distributions were accomplished for the detailed full-scale pantograph components. Good agreement was found between the obtained results and the reported results in the literature. Vortex shedding was the main source of noise at the pantograph panhead and knee. A modified model for the pantograph was introduced to reduce the aerodynamic noise of the pantograph’s panhead. A different design profile for the collector was presented as a possible solution for the reduction of both the aerodynamic noise and the reduction of the fluctuating forces at the panhead-catenary interaction, which affects the quality of the power transmitted to the high-speed train. The cylindrical cross-section of the panhead bars was replaced with different cross-sections. It was noticed that at a speed of 250 km/hr, the use of an elliptic cross-section has resulted in an almost 23.1% reduction in the acoustic sound pressure for the pantograph.

... Numerical investigations for a full-scale DSA350SEK pantograph were conducted by Yu et al. [29] who combined a nonlinear acoustic solver analysis with the FW-H acoustic analogy to predict the aerodynamic noise. Kim et al. [30] used the Improved version of DDES (IDDES) with an improved wall-modelling capability to model a pantograph mounted in different roof cavities with rounded or chamfered edges. ...

Aerodynamic noise from pantographs becomes an important source of noise from trains at high speeds. Previous studies have mostly been based on numerical predictions using computational aeroacoustic methods, which require large computing resources, or measurements conducted in a wind tunnel which cannot take all the real conditions into account. A component-based model relying on empirical constants obtained from the literature has been shown to predict aerodynamic noise from pantographs that agrees well with wind tunnel measurements. This model is extended in this paper by making use of simulation results on individual cylinders to refine the model constants and the Reynolds number dependence. In addition, allowance for the effect of incoming turbulence and cylinder aspect ratio is also extended. The updated model shows improved agreement with wind tunnel measurements, particularly at low frequencies. This model is then used to predict pantograph noise in more realistic conditions during train pass-by. The incoming flow conditions in terms of the incident flow speed, the turbulence intensity and the turbulence length scale are estimated from the literature considering the development of the boundary layer along the train roof. The sensitivity of the model to these assumptions is assessed using Monte Carlo simulations. The predicted results are compared with field measurements obtained using microphone array techniques for pantograph on different operational trains. Good agreement is obtained between the predictions and the measurements in terms of the far-field noise spectra and the dependence of noise level on speed. Differences are noted between measured levels for different orientations of the pantograph which according to the model are mainly related to the distance of the pantograph from the front of the train.

... Recently, numerical studies [9][10][11][12][13] were carried out on the aerodynamic noise of highspeed trains. In general, it has been reported that the first bogie, the pantograph, and the inter-coach space, are the primary aerodynamic noise sources of high-speed trains. ...

The interior noise of a high-speed train due to the external flow disturbance is more than ever a major problem for product developers to consider during a design state. Since the external surface pressure field induces wall panel vibration of a high-speed train, which in turn generates the interior sound, the first step for low interior noise design is to characterize the surface pressure fluctuations due to external disturbance. In this study, the external flow field of a high-speed train cruising at a speed of 300 km/h in open-field and tunnel are numerically investigated using high-resolution compressible LES (large eddy simulation) techniques, with a focus on characterizing fluctuating surface pressure field according to surrounding conditions of the cruising train, i.e., open-field and tunnel. First, compressible LES schemes with high-resolution grids were employed to accurately predict the exterior flow and acoustic fields around a high-speed train simultaneously. Then, the predicted fluctuating pressure field on the wall panel surface of a train was decomposed into incompressible and compressible ones using the wavenumber-frequency transform, given that the incompressible pressure wave induced by the turbulent eddies within the boundary layer is transported approximately at the mean flow and the compressible pressure wave propagated at the vector sum of the sound speed and the mean flow velocity. Lastly, the power levels due to each pressure field were computed and compared between open-field and tunnel. It was found that there is no significant difference in the power levels of incompressible surface pressure fluctuations between the two cases. However, the decomposed compressible one in the tunnel case is higher by about 2~10 dB than in the open-field case. This result reveals that the increased interior sound of the high-speed train running in a tunnel is due to the compressible surface pressure field.

In this paper, the unsteady flow around a high-speed train is numerically simulated by detached eddy simulation method (DES), and the far-field noise is predicted using the Ffowcs Williams-Hawkings (FW-H) acoustic model. The reliability of the numerical calculation is verified by wind tunnel experiments. The superposition relationship between the far-field radiated noise of the local aerodynamic noise sources of the high-speed train and the whole noise source is analyzed. Since the aerodynamic noise of high-speed trains is derived from its different components, a stepwise calculation method is proposed to predict the aerodynamic noise of high-speed trains. The results show that the local noise sources of high-speed trains and the whole noise source conform to the principle of sound source energy superposition. Using the head, middle and tail cars of the high-speed train as noise sources, different numerical models are established to obtain the far-field radiated noise of each aerodynamic noise source. The far-field total noise of high-speed trains is predicted using sound source superposition. A step-by-step calculation of each local aerodynamic noise source is used to obtain the superimposed value of the far-field noise. This is consistent with the far-field noise of the whole train model’s aerodynamic noise. The averaged sound pressure level of the far-field longitudinal noise measurement points differs by 1.92 dBA. The step-by-step numerical prediction method of aerodynamic noise of high-speed trains can provide a reference for the numerical prediction of aerodynamic noise generated by long marshalling high-speed trains.

The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD code. Then, the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based on Weld Planner software. The effects of welding sequence, clamping configuration and reverse deformation on welding distortion of floor structure were examined numerically. The results indicate that the established elastic FEM model for floor structure is reliable for predicting the distribution of welding distortion in view of the good agreement between the calculated results and the measured distortion for real double floor structure. Compared with the welding sequence, the clamping configuration and the reverse deformation have a significant influence on the welding distortion of floor structure. In the case of 30 mm reverse deformation, the maximum deformation can be reduced about 70% in comparison to an actual welding process.

The aerodynamic noise from a high-speed train becomes predominant at sufficiently high train speeds. Pantographs and bogies have been identified as significant aerodynamic noise sources in high-speed trains. The aerodynamic noise generated by pantographs is produced by a vortex shedding process while the aerodynamic noise from bogies is mainly generated by complex circulation of turbulent flow around its components. A semi-empirical component-based method for fast prediction of aerodynamic noise from a high-speed train pantograph is developed on the basis of similar models applied to landing gear noise prediction. Model predictions give good agreement with existing wind tunnel tests showing the approach to be promising. For the bogie, wind tunnel tests have been designed using a 1/10th scale bogie mock up. The results obtained are in agreement with existing data from train pass-by tests, showing that these experimental data can be used for model calibration and validation.

As a result of the "Speed Up" campaigns initiated in the end of last century when commercial train service averaged 48 km/h, China now has the world's longest high speed rail (HSR) network. In the past decade, China Railway High-speed (CRH) has undergone numerous technological innovation to ensure their safe, eco-friendly, and economical operation. With the privilege of involving in the construction and operation of such a large scale and long distance HSR network, researchers and engineers in the field have gained systematic and deep understanding about the dynamic system composed of train, wheels and rails, catenary and pantograph, and aerodynamic resistance. In this review paper, we summarize current research progress covering aerodynamics, catenary-pantograph interaction, dynamics and related issues of carbody, stability analysis, rail-wheel interaction, reliability of key components, and mechanisms about noise-generation. At the end, we supply our perspective about opportunities and challenges for future research and development on the mechanics of high speed rail.

A set of acoustic optimization design methods is established by combining the flow field deterioration theory and the acoustic analogy theory, and applied to the acoustic optimization design of high-speed train snow-plough. The results show that the streamline bodies of the head/tail car are the most important sound sources, respectively, accounting for 23.7% and 33.7% of the total sound energy. Compared with the streamline body of tail head, the streamline body of head car is more biased towards high frequency for the sound source energy. The A-weighted radiated noise of the train body is characterized by broadband sound (mainly in the range of 1–4 kHz) and peak features (especially at 2 kHz). The snow-plough with the maximum expansion length can mitigate the strong peak effect of the sound at 2 kHz, reduce the total sound energy, and show the best acoustic radiation performance in the four schemes. The numerical computation model was checked by the wind tunnel test results.

Flow induced noise increase significantly with speed, consequently noise reduction has become an important consideration for high-speed train designs. However, reducing noise from a train pantograph is more challenging because of the difficulty to shield it using rail side acoustic barriers. The flow behavior around a high-speed pantograph arm and train roof at a 1/10 scale is investigated using computational fluid dynamics. The geometries of the roof and the pantograph arm are simplified as a square shallow cavity and a straight cylinder, respectively. To resolve the details of the turbulent flow structures and hence enable accurate noise predictions, the improved delayed detached-eddy simulation is used in near-field modelling and Ffowcs-Williams & Hawkings aeroacoustics model is employed for far-field acoustic calculation. In this work, the influence of geometrical alteration at the cavity leading edge is considered. The results show that the recirculation vortices, which generate highly turbulent flow, decrease with increasing cavity leading edge roundness, and this reduces wall pressure fluctuations, which is a major noise source, on the cavity and cylinder surfaces. Furthermore, aerodynamics performance, such as drag, is improved. Finally, the effect of the arm positions is studied. No significant effect was found for overall sound pressure level, but tonal noise levels from the cylinder was reduced. A reduction of interaction between the lower part of the cylinder surface and cavity shear layers was detected, and it is believed that the reduction of interaction reduces the peak noise levels.

It is still difficult to conduct numerical calculation of the aerodynamic noise of full-scale, long-marshalling, high-speed trains. Based on the Lighthill acoustic analogy theory, the aerodynamic sound source of the high-speed train is equivalent to countless micro-vibrating sound sources. An acoustic radiation model of the dipole sound source of high-speed trains is established, and a method to predict the aerodynamic noise in the far field of long-marshalling high-speed trains is proposed. By this method, combined with numerical simulation technology, the flow field, noise source, and far-field noise characteristics of high-speed trains with different marshalling numbers are studied. The improved delayed detached eddy simulation method is used for flow field calculation, to obtain aerodynamic noise source information regarding the surface of high-speed trains. The numerical calculation method is verified by wind tunnel testing. The results show that the flow field and noise source characteristics of high-speed trains with different marshalling numbers are similar. The greater the length of the train body, the longer the trailing distance of the train wake, and the stronger of a surface noise source the tail car becomes. The spatial distribution characteristics of aerodynamic noise in the far field of high-speed trains do not change significantly with the length of the train body, but the magnitude of the sound pressure level will increase with the increase in length of the train body. The middle car body parts of high-speed trains with different marshalling numbers have similar noise distributions and sound pressure levels. Based on the noise calculation results of the 3-marshalling high-speed train, the far-field noise of the 5-marshalling and 8-marshalling train models is predicted and found to be in good agreement with the far-field noise of the actual train model. The differences in average sound pressure level are 1.01 dBA and 1.74 dBA, respectively.

Unsteady flow field and far-field noise generated by full-scale high-speed trains pantograph were predicted by large eddy simulation and FW-H equation, and analyzed by coherence and reduced-order analyses. The agreement between simulation and test of tandem square cylinder at close Reynolds number of 1.8 × 10⁵ indirectly validates the numerical method of full-scale pantograph. For the full-scale pantograph running at the speed of 300 km/h, the total sound pressure level radiated to the standard far-field receiver is 81.2 dB. The far-field noise radiated by the pan-head is more significant than that of the support rod and base frame, and the peak noise occurs at the frequencies of 252 Hz and 353 Hz. The coherence analysis shows that the peak noise frequency of 252 Hz generates near the knuckle of the pan-head and the upper arm, and that of 353 Hz generates in the middle position of the pan-head’s three rods, where there is a complete vortex shedding structure with positive and negative phase distribution. The reduced-order analysis shows that the first and second order modes containing the most energy represent the spatial vortex shedding around the pan-head. A typical wake flow with the frequency of 353 Hz is shed behind the pantograph rods, while an alternating vortex with the frequency of 252 Hz is shed on both sides of the rods.

As one of the main aerodynamic noise sources of high-speed trains, the pantograph is a complex structure containing many components, and the flow around it is extremely dynamic, with high-level turbulence. This study analyzed the near-field unsteady flow around a pantograph using a large-eddy simulation (LES) with high-order finite difference schemes. The far-field aerodynamic noise from a pantograph was predicted using a computational fluid dynamics (CFD)/Ffowcs Williams-Hawkings (FW-H) acoustic analogy. The surface oscillating pressure data were also used in a boundary element method (BEM) acoustic analysis to predict the aerodynamic noise sources of a pantograph and the far-field sound radiation. The results indicated that the main aerodynamic noise sources of the pantograph were the panhead, base frame and knuckle. The panhead had the largest contribution to the far-field aerodynamic noise of the pantograph. The vortex shedding from the panhead generated tonal noise with the dominant peak corresponding to the vortex shedding frequency and the oscillating lift force exerted back on the fluid around the panhead. Additionally, the peak at the second harmonic frequency was associated with the oscillating drag force. The contribution of the knuckle-downstream direction to the pantograph aerodynamic noise was less than that of the knuckle-upstream direction of the pantograph, and the average sound pressure level (SPL) was 3.4 dBA. The directivity of the noise radiated exhibited a typical dipole pattern in which the noise directivity was obvious at the horizontal plane of θ=0°, the longitudinal plane of θ=120°, and the vertical plane of θ=90°.

The quadrupole aerodynamic noise is a difficult problem in numerical simulation of the aerodynamic noise. The Kirchhoff-Ffowcs Williams and Hawkings (K-FWH) equation method and the three-dimensional compressible Large Eddy Simulation (LES) method are adopted in this manuscript for aerodynamic noise accuracy simulation of 600km/h high-speed train. The influence of different distributions of penetrable integral surfaces on the results of far-field aerodynamic noise is discussed. The optimum combination form of penetrable integral surfaces is obtained. The aerodynamic noise of high-speed train considering quadrupole can be calculated efficiently and accurately by using the upstream body surface and wake area penetrable integral surface as sound source surface. The wake area penetrable integral surface should contain the main vorticity structure of the wake as far as possible and the surface vorticity amplitude should be insignificant. The contribution rate of the dipole and quadrupole to the total aerodynamic noise energy of high-speed train is different. The aerodynamic noise energy of the upstream measurement points is mainly dipole aerodynamic noise energy, while that of the downstream measurement points is mainly dipole and quadrupole noise energy. The method proposed in this manuscript is of great significance in the aerodynamic noise numerical simulation of 600km/h high-speed train.

At typical speeds of modern high-speed trains the aerodynamic noise produced by the airflow over the pantograph is a significant source of noise. Although numerical models can be used to predict this they are still very computationally intensive. A semi-empirical component-based prediction model is proposed to predict the aerodynamic noise from train pantographs. The pantograph is approximated as an assembly of cylinders and bars with particular cross-sections. An empirical database is used to obtain the coefficients of the model to account for various factors: incident flow speed, diameter, cross-sectional shape, yaw angle, rounded edges, length-to-width ratio, incoming turbulence and directivity. The overall noise from the pantograph is obtained as the incoherent sum of the predicted noise from the different pantograph struts. The model is validated using available wind tunnel noise measurements of two full-size pantographs. The results show the potential of the semi-empirical model to be used as a rapid tool to predict aerodynamic noise from train pantographs.

Due to the limited understanding of spatial sound field and contribution of pantograph, a deep analysis is presented to extract understanding the aerodynamic noise characteristics of high-speed trains pantograph system. The near-field and far-field noise are predicted by the acoustic perturbation equations and Ffowcs Williams-Hawkings equation, respectively. The spatial sound propagation is analyzed by proper orthogonal decomposition and cluster-based reduced-order modelling. The flow field results predicted by large eddy simulation show that the flow behind pantograph is governed by hierarchical structures, which occurs to be featured with three layers as well as periodic evolution. The dipole source is dominated in far-field radiated noise while the quadrupole source is negligible, since the intensity of the quadrupole source is less than that of the dipole source. The contribution rates of base-frame, pan-head, groove, upper-arm, horn, lower-arm and rod-insulator are higher than the other components, and the radiated sound energy of them accounts for approximately 90% of the total energy. The noise contribution of pan-head exceeds 10% at the frequency of 1000 Hz. Base-frame is the largest contributor, and more than 6% of noise contribution occurs at the frequency of 630 Hz. The spatial sound propagation includes two major aspects: one is mainly reflected upwind from groove, and the other is propagated with the center of groove. The results highlight the possibility to develop a new design of high-speed trains pantographs, in order to obtain an aerodynamic noise reduction.

In order to study the effect of the strip spacing on the aerodynamic noise characteristics of the pantograph of high-speed train, the numerical simulation of the aerodynamic flow behavior for the high-speed pantograph is conducted using the detached eddy simulation (DES) and its aerodynamic noise is studied using the FW-H model. The numerical method is verified by flows around a cylinder with a finite span. The numerical results show that the strip spacing has a great effect on the aerodynamic characteristics of the pantograph. When there is only one strip, the aerodynamic drag force is reduced by 10.4% compared with the double-strip pantographs. The fluctuation in pressure on the strip and the fluctuation in lift force of the panhead are the smallest. The aerodynamic drag force of the double-strip pantograh increase with the incremental of the strip spacings. Under different strips spacings, the vortex structure around the panhead is different, and the inappropriate strip spacing will aggravate the fluctuation in forces due to the vortex shedding from the strip. The vortex shedding frequencis are mainly 270Hz, 540Hz, 820Hz. Meanwhile, the strip spacing has few effect on the frequency of vortex shedding. The radiated noise from the pantograph is transmitted in the form of a spherical wave. When the strip spacing is 0 mm or 540 mm, the sound pressure level of the far field radiation noise of the pantograph is smaller. The energy of the far field aerodynamic noise of the pantograph is mainly concentrated in the frequency range of 200–1600 Hz. For a pantograph with double-strip, when the spacing is 540 mm, the sound pressure level at the noise measurement point (25m, 0, 3.5m) is the smallest. Whereas the strip spacing is 475 mm, the sound pressure level is the largest and the difference reaches 2.8 dBA.

The aerodynamic noise of high-speed trains increases significantly under crosswinds. Researches have typically focused on the characteristics of aerodynamic loads and the corresponding safety issues, with less attention to flow-induced noise characteristics. In the present paper, the near-field unsteady flow behaviour around a pantograph was analysed using a large eddy simulation. The far-field aerodynamic noise from a pantograph was predicted using the Ffowcs Williams-Hawkings acoustic analogy. The results showed that asymmetric characteristics of the flow field could be observed using the turbulent kinetic energy and the instantaneous vortexes in crosswind conditions. Vortex shedding, flow separation and recombination around the pantograph were the key factors for aerodynamic noise generation. The directivity of the noise radiation was inclined towards the leeward side of the pantograph. The aerodynamic noise propagation pattern can be considered as a typical point source on spherical waves when the transverse distance from the pantograph geometrical centre is farther than 8 m. The sound pressure level grew approximately as the 6th power of the pantograph speed. The peak frequency exhibited a linear relationship with the crosswind velocity. The numerical simulation results and wind tunnel experiments had high consistency in the full frequency domain, namely, the peak frequency distribution range, the main frequency amplitude and the spectral distribution shape.

The object of study in this paper is the Faiveley CX-PG pantograph. We first used the large-eddy simulation (LES) model to simulate the surrounding fluctuating flow field. We then identified the vortex structures in the flow field of the pantograph via the Q criterion, and performed a Fourier transform on the fluctuating pressure. We finally used the Ffowcs Williams-Hawkings (FW-H) equation to predict the far-field radiation noise of the pantograph. Through these steps, we explored the vortex structures in the flow field of the pantograph, aeroacoustic performance of the pantograph's main components, and the relationship between them, and proposed corresponding acoustic optimization countermeasures. The results showed that the vortex structures in the flow field of the pantograph varied with time and had a certain periodicity, and that the sound source intensity of the pantograph was mainly distributed in the bottom frame, three insulators, balance beam, upper arm frame, and lower arm. The sound source energy of these components accounted for approximately 92% of the total energy; the influencing factors for the aerodynamic sound source intensity of the pantograph included the shedding positions and vorticities of the vortex structures as well as whether it was located in the wake of the vortex structures. The aerodynamic noise of the pantograph could be effectively controlled by adjusting the vortex shedding position, reducing the vorticities of the vortex structures, increasing the distance between the mutually interfering components, setting the diversion structure to control the discharge area of the vortex structures. The sound source energy of the bottom frame area accounted for more than 50% of the total energy; a settlement platform or shroud could be installed to effectively control the noise in the area, thereby effectively reducing the noise radiated by the pantograph. The simulation results in this paper were in good agreement with the wind tunnel test results and theoretical results, and can provide a reference for the optimal design of future acoustics for the pantograph.

In order to improve the aerodynamic performance of the pantograph fairing of a high-speed train, an aerodynamic shape optimization design approach of the pantograph fairing was proposed based on a multi-objective genetic algorithm and the theory of computational fluid dynamics (CFD). The aerodynamic drag force and the acoustic power level of the fairing were set to be the optimization objectives. A three-dimensional (3D) parametric model of the pantograph fairing was established and 4 optimization design variables were extracted. The script files of the software of CATIA and STAR-CCM+ were integrated into the optimization design software ISIGHT, and then the automatic deformation of the pantograph fairing and the automatic calculation of the train aerodynamics could be obtained. The design variables were automatically updated by non-dominated sorting genetic algorithm-II (NSGA-II) to achieve the automatic optimization of the pantograph fairing. After optimization, the correlations between the optimization objectives and the design variables were analyzed, and the most important design variables which influenced the optimization objectives were obtained. The optimization results show that the correlations between the optimization design variables and the two optimization objectives are the same, and only the values of the correlation coefficients are different. Compared with the prototype, the aerodynamic drag force of the middle coach with the optimized fairing has been reduced up to 4.21%, and the maximum acoustic power level of the optimized fairing has been reduced up to 7.38%.

In this study, a large-eddy simulation (LES) with high-order finite difference schemes and Ffowcs Williams-Hawkings (FW-H) acoustic analogy method was utilized to investigate the aerodynamic noise characteristics of a high-speed train pantograph. The surface oscillating pressure data were also used in a boundary element method (BEM) acoustic analysis to predict aerodynamic noise sources of a pantograph and the sound radiation. The far-field noise radiation of the pantograph, considering both the two main operating orientations of a pantograph (the knuckle-upstream and knuckle-downstream directions), and the aerodynamic noise of the pantograph, was compared. Results of numerical investigations showed that the main harmonic frequencies were 342, 691, 1030 Hz (when the pantograph was running at a speed of 400 km/h). And the noise radiations from the knuckle-downstream direction of the pantograph were 3.6, 5.8, and 0.4 dB lower than those of the knuckle-upstream direction at frequencies of 342, 691, and 1030 Hz, respectively.

Reducing train pantograph noise is particularly important. In this paper, the flow behaviour and noise contribution of simplified geometries representing high-speed train pantographs and the roof cavity at 1/10th scale are investigated. The Improved Delayed detached-Eddy Simulation (IDDES) turbulent model is used for the flow field simulation and the Ffowcs Williams & Hawkings aeroacoustic analogy is used for far-field noise prediction. The pantograph recess geometry is simplified to a rectangular cavity and two simplified DSA350 pantographs are included. The effect of the pantograph cavity is studied by comparing the flow behaviour and radiated noise from cases with and without the cavity, and also for different train running directions. When the pantographs are installed in a cavity, the shear layer, separated from the cavity leading edge, interacts with the pantographs, and generates large pressure fluctuations on the pantograph surfaces. In comparison with pantographs installed on a flat train roof, the flow around the pantographs with the cavity has different characteristics in terms of the velocity profile upstream of the pantographs. The study shows that the main noise source is from the panhead of the raised pantograph which produces strong tonal noise and this noise source is affected by the cavity flow.

The behavior of two dimensional vortex pairs (VP), either co-rotating or counter-rotating, are investigated numerically using a lattice Boltzmann method (LBM). The aero-acoustic phenomena induced by vortical flows are analyzed. Regarding the co-rotating VP in free space, we find that the fore-collapse and after-collapse stages are governed by total circulation conservation and viscous diffusion, respectively. Our numerical results are consistent with Lighthill's and Möhring's predictions, which are based on measured quantities. On the other hand, when a wall is present near the co-rotating VP, viscous effects play important roles in vortex motion. The vortex motion undergoes freely rotating, merging, and rebounding stages sequentially. The far field sound synchronizes with the vortex motion. Next, we simulate the impact of a counter-rotating VP on a flat wall. It is shown that sound emission relates closely to the trajectory of the VP. Meanwhile, the rebound of the vortex is essentially induced by the shedding of the secondary (or tertiary) vortex from the boundary layer. Based on the results, we show that the lattice Boltzmann method is extremely suitable for describing sound signals from vortical flows.

Some numerical solutions of acoustic propagation problems using linearized Euler equations are studied. The two-dimensional Euler equations are linearized around a known stationary mean ow. The computed solution is obtained by using a dispersion-relation-preserving scheme in space, combined with a fourth-order Runge–Kutta algorithm in time. This numerical integration leads to very good results in terms of accuracy, stability, and low storage. The implementation of source terms in these equations is studied very carefully in various con gurations, inasmuch as the nal goal is to improve and to validate the stochastic noise generation and radiation model. In this approach, the turbulent velocity eld is modeled by a sum of random Fourier modes through a source term in the linearized Euler equations to predict the noise from subsonic ows. The radiation of a point source in a subsonic and a supersonic uniform mean ow is investigated. The numerical estimates are shown to be in excellent agreement with the analytical solutions. Then, the emphasis is on the ability of the method to describe correctly the multipolar structure of aeroacoustic sources. The radiation of dipolar and quadrupolar extended sources is, thus, studied. Next, a typical problem in jet noise is considered with the propagation of acoustic waves in a sheared mean ow. The numerical solution compares favorably with ray tracing. Finally, a nonlinear formulation of Euler's equations is solved to limit the growth of instability waves excited by the acoustic source terms.

Airfoil self-noise is a common phenomenon for many engineering applications. Aiming to study the underlying mechanism of airfoil self-noise at low Mach number and moderate Reynolds number flow, a numerical investigation is presented on noise generation by flow past NACA0018 airfoil. Based on a high-order accurate numerical method, both the near-field hydrodynamics and the far-field acoustics are computed simultaneously by performing direct numerical simulation. The mean flow properties agree well with the experimental measurements. The characteristics of aerodynamic noise are investigated at various angles of attack. The obtained results show that inclining the airfoil could enlarge turbulent intensity and produce larger scale of vortices. The sound radiation is mainly towards the upper and lower directions of the airfoil surface. At higher angle of attack, the tonal noise tends to disappear and the noise spectrum displays broad-band features.

In order to investigate the noise level, major sound sources and their distribution characteristics of 350 km·h-1 high-speed train in operation, based on the current theoretical and experimental experience of high-speed train noise, a testing site is selected on Jing-Jin Inter-City high-speed railway, at which the status of the train and the track are satisfied with the correlative condition of ISO3095-2005. The field test of high-speed train noise is carried out through using the data acquisition and analysis system of multi-channel microphone array for high-speed railway noise. The testing results show that the major sound sources of the emitting noise from 350 km·h-1 high-speed train are the wheel/rail rolling noise and the aerodynamic noise from the bogie, the equipments and recess of the pantograph, and the inter-coach spacing. The first four sound sources of the SEL curves corresponding to the eight vehicles refer, in turn, to the wheel/rail contact area of the first vehicle, the pantograph on the second vehicle, the wheel/rail contact area of the second vehicle, and the aerodynamic noise from the up-part of the first two vehicles. Finally, several countermeasures are proposed to control 350 km·h-1 high-speed train noise based on the testing results.

Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA Scientific and Technical Information (STI) Program Office plays a key part in helping NASA maintain this important role. The NASA STI Program Office is operated by Langley Research Center, the lead center for NASA's scientific and technical information. The NASA STI Program Office provides access to the NASA STI Database, the largest collection of aeronautical and space science STI in the world. The Program Office is also NASA's institutional mechanism for disseminating the results of its research and development activities. These results are published by NASA in the NASA STI Report Series, which includes the following report types: • TECHNICAL PUBLICATION. Reports of completed research or a major significant phase of research that present the results of NASA programs and include extensive data or theoretical analysis. Includes compilations of significant scientific and technical data and information deemed to be of continuing reference value. NASA counterpart of peer-reviewed formal professional papers, but having less stringent limitations on manuscript length and extent of graphic presentations. • TECHNICAL MEMORANDUM. Scientific and technical findings that are preliminary or of specialized interest, e.g., quick release reports, working papers, and bibliographies that contain minimal annotation. Does not contain extensive analysis.

Three types of pantograph horn model; simple cylinder, a cylinder with periodic holes and a cylinder with a continuous slit, are tested in a low noise wind tunnel to compare their characteristics of aerodynamic noise and flow fields in the wake. Formation of strong vortices of alternate sign that have large structure in the spanwise direction is suppressed due to the flow through holes or the slit. The cylinder with the continuos slit is proved to reduce the noise sufficiently, but an unstable flow through the slit seems to produce distinct noise. Since formation of strong vortices is mainly suppressed due to momentum injection through holes or the slit, periodic holes have little effect on collapsing the spanwise structure of vortices, but they contribute to making the flow around the horn stable. The shape of holes should be optimized to avoid strong acoustic resonance.

The aerodynamic noise radiation from a vestibule side door on a high-speed train surface is calculated by the combination of unsteady incompressible fluid flow analysis and acoustic analysis. Pressure fluctuation on a vestibule side door surface is measured to verify the results of fluid flow analysis. Analysis results agree with measured data very well at low frequencies. For high-frequency components, the solvable frequency is limited by the analysis mesh size. Required mesh size is typically one eighth of the wavelength of the pressure fluctuation on the model surface. The aerodynamic noise is mainly radiated from around the following corner where the vortices that are shed from the leading corner strongly interact with the train surface.

Environmental requirements for railway operations will become tighter in the future. In particular, annoyance due to railway noise has to be taken carefully into account in the expansion of freight traffic as well as in new high speed line projects. Reduction of noise at source can be more attractive than the use of noise barriers but this requires a thorough understanding of the source mechanisms. This paper presents a critical survey of the identification and modelling of railway noise sources and summarizes the current knowledge of the physical source phenomena (mainly rolling and aerodynamic sources) as well as the potential for noise reduction. Future research perspectives are also given. These concern, in particular, improvements to source modelling, especially for aerodynamic noise, investigation of other sources and development of more advanced models for predicting railway noise in the environment. These should include a better description of the sources, obtained from modelling.

A theory is initiated, based on the equations of motion of a gas, for the purpose of estimating the sound radiated from a fluid flow, with rigid boundaries, which as a result of instability contains regular fluctuations or turbulence. The sound field is that which would be produced by a static distribution of acoustic quadrupoles whose instantaneous strength per unit volume is rho vivj + pij - a02rho delta ij, where rho is the density, vi the velocity vector, pij the compressive stress tensor, and a0 the velocity of sound outside the flow. This quadrupole strength density may be approximated in many cases as rho 0vivi. The radiation field is deduced by means of retarded potential solutions. In it, the intensity depends crucially on the frequency as well as on the strength of the quadrupoles, and as a result increases in proportion to a high power, near the eighth, of a typical velocity U in the flow. Physically, the mechanism of conversion of energy from kinetic to acoustic is based on fluctuations in the flow of momentum across fixed surfaces, and it is explained in section 2 how this accounts both for the relative inefficiency of the process and for the increase of efficiency with U. It is shown in section 7 how the efficiency is also increased, particularly for the sound emitted forwards, in the case of fluctuations convected at a not negligible Mach number.

Shinkansen noise consists of various noise sources, such as the rolling noise, concrete bridge structure noise, aerodynamic noise and so on. Among these, the aerodynamic noise is the most important at speeds over 270km/h in some cases because of its strong dependence on train speed. Thus it is necessary to clarify the characteristics of the aerodynamic noise generated by high speed trains for noise reduction. In this paper, wind tunnel tests using a 1/5 scale Shinkansen train model were performed. An acoustic mirror, which consists of an omni-directional microphone and a reflector, was chosen as a measuring device. First, the principle and characteristics of the acoustic mirror are discussed and a method of estimating quantitatively the aerodynamic noise generated by each part of the model is proposed on the basis of wind tunnel test data. Next, the distribution of aerodynamic noise sources generated by the 1/5 scale Shinkansen train model is shown, based on which the contribution of individual noise sources of Shinkansen trains to the wayside noise level is estimated. Finally, the noise source distribution of real Shinkansen trains was measured with the acoustic mirror in a field test. The results of the field test show a good agreement with those of the wind tunnel tests.

Annoyance due to railway noise is a particularly sensitive aspect of new high-speed projects. Many studies have shown that aerodynamic noise becomes significant above 300 km/h and can become predominant with the reduction of the contribution of rolling noise. At the moment, no further global reduction of high-speed train noise can be achieved if the aerodynamic noise is not reduced. The objective of this paper is to provide a critical survey of the aeroacoustic noise problem for trains, particularly for high-speed trains. The first step in any acoustic study is to identify the different sources. This paper describes the different aeroacoustic phenomena which are representative of high-speed trains and the technical methodologies used to characterize these phenomena. Specific tools have been developed from on-line tests, wind tunnel experiments, theoretical studies or numerical simulations to characterize the different sources. Using examples, the limitations of the methods and the solutions currently available are reveiwed today. Methods of global modelling of a high-speed train emission are also presented. Finally, future development of new tools based on numerical simulation in aeroacoustics are discussed.

Physical arguments are followed by mathematical developments to show how aerodynamic sound is generated as a result of the movement of vortices, or of vorticity, in an unsteady fluid flow. Changes in circulation or area of a vortex ring give rise to a dipole sound field, the former being illustrated by oscillating flow about a fixed sphere, and the latter by a simple model for the aeolian tone attributable to the stretching of vortex rings. Because in a free flow there can be no change of the total vortex strength (circulation times area), there is no net dipole strength, but each moving element of vorticity still causes local dipolelike flow; each element of moving vorticity acts with some equal and opposite movement elsewhere in the flow so that together they form an oblique quadrupole, although the total effect must be reducible to an assembly of lateral quadrupoles. A cardinal result is that the vorticity in a slightly compressible fluid can be considered to induce the whole flow field, both the hydrodynamic part and the acoustic part. With vorticity taken as the common basis, a slightly compressible flow is compared to the corresponding incompressible one, which may be used in the evaluation of the sound‐radiation formula. The theory is particularly well‐structured to estimate sound from flows described in terms of vorticity: the sound field is determined for two rectilinear vortices spinning about an axis between them, and its basis for similarity methods is demonstrated in application to free shear flow and jet flow.

In order to reduce the pantograph noise that greatly contributes to overall noise, we have developed two types of low-noise pantograph. Further noise reduction was realized by the effects of attenuation of the pantograph noise insulation plate and by using only one pantograph per trainset. A multi-segment slider was also developed to increase the performance of following the overhead contact wire, which is imperative when running with only one pantograph per trainset. These countermeasures for pantograph noise have been installed on FASTECH 360 (high-speed test trains of East Japan Railway Company). The results measured by use of a microphone array show that the pantograph peak noise level is reduced by more than 2 dB compared to that of the series E2 trains now in operation.

The noise value (A -weighted sound pressure level, SLOW) generated by Shinkansen trains, now running at 220–300 km/h, should be less than 75 dB(A) at the trackside. Shinkansen noise, such as rolling noise, concrete support structure noise, and aerodynamic noise are generated by various parts of Shinkansen trains. Among these aerodynamic noise is important because it is the major contribution to the noise generated by the coaches running at high speed. In order to reduce the aerodynamic noise, a number of improvements to coaches have been made. As a result, the aerodynamic noise has been reduced, but it still remains significant. In addition, some aerodynamic noise generated from the lower parts of cars remains. In order to investigate the contributions of these noises, a method of analyzing Shinkansen noise has been developed and applied to the measured data of Shinkansen noise at speeds between 120 and 315 km/h. As a result, the following conclusions have been drawn: (1) Aerodynamic noise generated from the upper parts of cars was reduced considerably by smoothing car surfaces. (2) Aerodynamic noise generated from the lower parts of cars has a major influence upon the wayside noise.

The three-dimensionality of the vortex shedding from a circular cylinder at high subcritical Reynolds number (4.3×104) has been studied, focusing on the characteristics of the vortex shedding phase drift and correlation along the cylinder span. Short time integration of the correlation coefficient, based on eight shedding cycles, showed that there were strong oscillations in the degree of correlation of the vortex shedding, and that these oscillations showed strong regularity having periods around 10–20 times the Strouhal period. These oscillations started when exceeding separations of Δz/d≊1 between the measurement points, and remained up to the largest case studied (Δz/d=6). The phase drift angle between two points at different spanwise positions was analyzed, showing that at the transition separation (Δz/d≊1) the probability distribution changed from being narrow banded to become more broad banded and closely Gaussian for an intermediate spacing of 2

A unified approach is used to derive many of the current formulas for calculation of discrete frequency noise of helicopter rotors and propellers. Both compact and noncompact results are derived. The noncompact results are based on the solution of Ffowcs Williams-Hawkings (FW-H) equation. The compact formulations are obtained as the limit of noncompact source results. In particular, the linearized acoustic theories of Hawkings and Lowson, Farassat, Hanson, Woan and Gregorek, Succi, and Jou are discussed in this paper. An interesting thickness noise formula by Isom and its extension by Ffowcs Williams are also presented.

Measurements have been made of the mean and fluctuating pressure distributions on long circular cylinders, having smooth and rough surfaces, at Reynolds numbers of 1·11 × 105 and 2·35 × 105 in both uniform and turbulent streams. The presence of free-stream turbulence a t these Reynolds numbers was found to suppress coherent vortex shedding on the smooth cylinder and give rise to a complex pressure field in which the mean pressure distribution was almost independent of Reynolds number over the small range of Reynolds numbers tested. The pressure distributions on the rough cylinder were found to be completely different in uniform and turbulent streams; the presence of turbulence gave rise to an increase in the level of vortex shedding energy, and produced mean pressure distributions similar to those obtained on smooth cylinders at Reynolds numbers of the order of 107.

Finite element and boundary element calculations are combined to predict the flow noise radiated from a 1/10th-scale model of an aerodynamic cover used around the pantograph on a train at 250 km h−1. The solutions of the unsteady air flow over the cover and the resulting sound propagation are divided into two parts in order to keep the problem tractable. First the unsteady fluid flow is solved using large-eddy simulation (LES). The pressure histories on the cover are then used to predict the radiated sound, using a boundary element method to solve the Helmholtz equation. The result thus leans heavily on assumptions about the coupling of the two solutions, the propagation of sound in a disturbed medium and the efficacy of LES. The predicted sound pressure levels are compared with experimental measurements made in an anechoic wind tunnel. © 1997 John Wiley & Sons, Ltd.

A low Mach number rod-airfoil experiment is shown to be a good benchmark for numerical and theoretical broadband noise modeling. The benchmarking approach is applied to a sound computation from a 2D unsteady-Reynolds-averaged Navier–Stokes (U-RANS) flow field, where 3D effects are partially compensated for by a spanwise statistical model and by a 3D large eddy simulation. The experiment was conducted in the large anechoic wind tunnel of the Ecole Centrale de Lyon. Measurements taken included particle image velocity (PIV) around the airfoil, single hot wire, wall pressure coherence, and far field pressure. These measurements highlight the strong 3D effects responsible for spectral broadening around the rod vortex shedding frequency in the subcritical regime, and the dominance of the noise generated around the airfoil leading edge. The benchmarking approach is illustrated by two examples:
the validation of a stochastical noise generation model applied to a 2D U-RANS computation;
the assessment of a 3D LES computation using a new subgrid scale (SGS) model coupled to an advanced-time Ffowcs–Williams and Hawkings sound computation.
In both cases, the ability of computational fluid dynamics to model the source mechanisms and of the CAA approach to predict the far field are assessed separately.

East Japan Railway Company has developed the high-speed test train “FASTECH360” for future speed-increase of the Shinkansen.
Noise reduction is one of the most important issues to be resolved in such a case. The test train equips several countermeasures
to reduce noise such as low-noise pantograph, pantograph noise insulation plates, sound absorbing panels. Moreover, the car
body has been made as smooth as possible to reduce aerodynamic noise. Snow plow covers, circumferential bellows, smoothed
doors on the drever’s cab are some of the examples of the smoother surface. As a result of running tests up to 360km/h, it
is confirmed that the noise from the test trains at a speed of approximately 330km/h is as almost equal to that of present
commercial trains at a speed of 275km/h (at a distance of 25m from the track).

For a high-speed train operating at 300km/h or more, the aerodynamic noise, which is induced by the pressure fluctuations of the air, reaches similar levels to the rolling noise, which is due to contact between the rail and wheel. For this reason, the study of the noise generated by the flow around the train is of great interest for the constructors and operators of high-speed trains. Although the main noise sources are now well identified, their localization is so far mainly based on experimental techniques using acoustic array measurements, applied either on small-scale models in a wind tunnel or on full-scale passing trains. Nonetheless, the numerical prediction of the aerodynamic noise is becoming more and more of a practical possibility, as the need is emerging for proper integration of technical solutions and optimizations at an early stage of design of new rolling stock.
In this study, the aerodynamic noise generated by the power car of the TGV POS high-speed train is considered. This generation of TGV is named POS for Paris Ost-Frankreich Süd-Deutschland as it has been dedicated to connect Paris to the East of France (Strasbourg) and the South of Germany (Stuttgart, Munich). It has been introduced on the French and German high-speed network in 2007, where the operational speed has been increased from 300km/h to 320km/h (on French East-European line).
For the two main reasons of the introduction of new rolling stock and the increase in speed, the aerodynamic noise is less well known and is expected to be more significant. A numerical study has been carried out to identify the sources of the noise and to quantify their level. Some results will be presented here.
In order to obtain results of a high level of quality, a very detailed geometry was used, and the unsteady simulations were carried out at full scale. The complexity of the real geometry and the consideration of all parts and elements of bogie or pantograph frames enabled the influence to be determined of several shape modifications or of the integration of fairings on the level of aerodynamic noise. This gives some clues for solutions in terms of noise reduction. Among all the solutions tested, two examples have been selected and are presented in this paper.

In this study, we propose techniques for reducing the noise from gaps between Shinkansen cars based on the results of noise
source localization in wind tunnel testing. In order to obtain the accurate noise source distributions, the microphone array
is installed near the train model. The influence of the shear layer around the main flow on the directivity of the microphone
array is clarified so that the microphone array should be set in the shear layer rather than the outside of the flow. Analysis
of the noise source localization reveals the principal noise sources around the gap, which suggests efficient approaches to
the noise reduction. Firstly, we found that the noise level of the gap section with rounded edge can be effectively reduced
by approximately 7 dB compared with that of the case with current condition. We also confirmed qualitatively the effect of
noise reduction techniques for the gap section by the field test.

The performance of sulfate-dependent anaerobic ammonium oxidation was studied. The results showed that both SO4
2− and NH4
+ were chemically stable under anaerobic conditions. They did not react with each other in the absence of biological catalyst
(sludge). The anaerobic digested sludge cultivated in an anaerobic reactor for three years took on the ability of oxidizing
ammonium with sulfate anaerobically. The average reduction of sulfate and ammonium was 71.67 mg·L−1 and 56.82 mg·L−1 at high concentrations. The reaction between SO4
2− and NH4
+ was difficult, though feasible, due to its low standard Gibbs free energy change. The experiment demonstrated that high substrate
concentrations and low oxidation-reduction potential (ORP) may be favourable for the biological reaction.

To reduce aerodynamic noise generated by a pantograph, which is one of the dominant noise sources of high-speed trains, the
authors proposed some noise reduction techniques, that is, shape-optimization of a panhead, relaxation of aerodynamic interference
between panhead and articulated frame and surface covering with porous material. To evaluate total noise reduction effect
of them, wind tunnel tests were performed with a prototype pantograph to which these techniques were applied. The test results
show that noise level of the prototype pantograph is lower than that of the currently-used pantograph by about 4 dB. Furthermore,
it was also confirmed that the prototype pantograph has enough aerodynamic stability against change of attack angle.

The general focus of this aerodynamic noise research, induced by turbulent incompressible flow, is to improve our knowledge of acoustic production mechanisms in the TGV pantograph recess in order to be able to reduce the radiated noise. This work is performed under contract with SNCF as a part of the German–French Cooperation DEUFRAKO K2, and is supported by French Ministries for Transport and Research. Previous studies on TGV noise source locations (DEUFRAKO K) have identified the pantograph recess as one of the important aerodynamic noise sources, for speeds higher than 300 km/h, due to flow separation. The pantograph recess is a very complex rectangular cavity, located both on the power car and the first coach roofs of the TGV, and has not been studied before due to the complex shapes. Its aeroacoustic features are investigated experimentally in a low-subsonic wind tunnel, on a realistic 1/7th scale mock-up both with and without pantographs. Flow velocities, estimated with hot-wire anemometry, and parietal visualizations show the flow to reattach on the recess bottom wall and to separate again at the downstream face. Wall pressure fluctuations and “acoustic” measurements using and in microphones respectively are also measured to qualify the flow: no aerodynamic or acoustic oscillations are observed. The study indicates that the pantograph recess has a different behaviour compared to the usual cavity grazing flows.

A review of propeller noise prediction technology is presented which highlights the developments in the field from the successful attempt of Gutin to the current sophisticated techniques. Two methods for the prediction of the discrete frequency noise from conventional and advanced propellers in forward flight are described. These methods developed at MIT and NASA Langley Research Center are based on different time domain formulations. Brief description of the computer algorithms based on these formulations are given. The output of these two programs, which is the acoustic pressure signature, is Fourier analyzed to get the acoustic pressure spectrum. The main difference between the programs as they are coded now is that the Langley program can handle propellers with supersonic tip speed while the MIT program is for subsonic tip speed propellers. Comparisons of the calculated and measured acoustic data for a conventional and an advanced propeller show good agreement in general.

Several expressions for the determination of the acoustic field of moving bodies are presented. The analysis is based on the Ffowcs Williams-Hawkings equation. Applying some proposed criteria, one of these expressions is singled out for numerical computation of acoustic pressure signature. The compactness of sources is not assumed and the main results are not restricted by the observer position. The distinction between compact and noncompact sources on moving surfaces is discussed. Some thickness noise calculations of helicopter rotors and comparison with experiments are included which suggest this mechanism as the source of high-speed blade slap of rotors.

Generalized functions have many applications in science and engineering. One useful aspect is that discontinuous functions can be handled as easily as continuous or differentiable functions and provide a powerful tool in formulating and solving many problems of aerodynamics and acoustics. Furthermore, generalized function theory elucidates and unifies many ad hoc mathematical approaches used by engineers and scientists. We define generalized functions as continuous linear functionals on the space of infinitely differentiable functions with compact support, then introduce the concept of generalized differentiation. Generalized differentiation is the most important concept in generalized function theory and the applications we present utilize mainly this concept. First, some results of classical analysis, are derived with the generalized function theory. Other applications of the generalized function theory in aerodynamics discussed here are the derivations of general transport theorems for deriving governing equations of fluid mechanics, the interpretation of the finite part of divergent integrals, the derivation of the Oswatitsch integral equation of transonic flow, and the analysis of velocity field discontinuities as sources of vorticity. Applications in aeroacoustics include the derivation of the Kirchhoff formula for moving surfaces, the noise from moving surfaces, and shock noise source strength based on the Ffowcs Williams-Hawkings equation.

One of the active areas of computational aeroacoustics is the application of the Kirchhoff formulas to the problems of the rotating machinery noise predictions. The original Kirchhoff formula was derived for a stationary surface. In 1988, Farassat and Myers derived a Kirchhoff Formula obtained originally by Morgans using modem mathematics. These authors gave a formula particularly useful for applications in aeroacoustics. This formula is for a surface moving at subsonic speed. Later in 1995 these authors derived the Kirchhoff formula for a super-sonically moving surface. This technical memorandum presents the viewgraphs of a day long workshop by the author on the derivation of the Kirchhoff formulas. All necessary background mathematics such as differential geometry and multidimensional generalized function theory are discussed in these viewgraphs. Abstraction is kept at minimum level here. These viewgraphs are also suitable for understanding the derivation and obtaining the solutions of the Ffowcs Williams-Hawkings equation. In the first part of this memorandum, some introductory remarks are made on generalized functions, the derivation of the Kirchhoff formulas and the development and validation of Kirchhoff codes. Separate lists of references by Lyrintzis, Long, Strawn and their co-workers are given in this memorandum. This publication is aimed at graduate students, physicists and engineers who are in need of the understanding and applications of the Kirchhoff formulas in acoustics and electromagnetics.

In this paper, we start with the definition of generalized functions as continuous linear functionals on the space of infinitely differentiable functions with compact support. The concept of generalization differentiation is introduced next. This is the most important concept in generalized function theory and the applications we present utilize mainly this concept. First, some of the results of classical analysis, such as Leibniz rule of differentiation under the integral sign and the divergence theorem, are derived using the generalized function theory. It is shown that the divergence theorem remains valid for discontinuous vector fields provided that the derivatives are all viewed as generalized derivatives. This implies that all conservation laws of fluid mechanics are valid as they stand for discontinuous fields with all derivatives treated as generalized deriatives. Once these derivatives are written as ordinary derivatives and jumps in the field parameters across discontinuities, the jump conditions can be easily found. For example, the unsteady shock jump conditions can be derived from mass and momentum conservation laws. By using a generalized function theory, this derivative becomes trivial. Other applications of the generalized function theory in aerodynamics discussed in this paper are derivation of general transport theorems for deriving governing equations of fluid mechanics, the interpretation of finite part of divergent integrals, derivation of Oswatiitsch integral equation of transonic flow, and analysis of velocity field discontinuities as sources of vorticity. Applications in aeroacoustics presented here include the derivation of the Kirchoff formula for moving surfaces,the noise from moving surfaces, and shock noise source strength based on the Ffowcs Williams-Hawkings equation.

General features of radiated field by source distributions in arbitrary motion and of sound generated by turbulent flow around high speed aerodynamic surface; Lighthill-Curle theory of aerodynamic sound is extended to artitrary motion; Kirchhoff description of homogeneous wave field is also generalized; at high supersonic convective speeds, field is dominated by intensive beaming along directions of Mach wave emission that lie normal to surface; surface-induced intensity increases as square of surface speed at high supersonic speeds.

Reduction of pantograph noise

- T Kurita
- M Hara
- M Horiuchi

Kurita, T., Hara, M., Horiuchi, M.: Reduction of pantograph noise. JR EAST Technical Review 8, 19–22 (2006)

The numerical prediction of the aerodynamic noise of the TGV POS high-speed train power car Noise and Vibration Mitigation for Rail Transportation Systems, Notes on Numer-ical Fluid Mechanics and Multidisciplinary Design

- E Masson
- N Paradot
- E Allain

Masson, E., Paradot N., Allain, E.: The numerical prediction of the aerodynamic noise of the TGV POS high-speed train power car. In: Maeda, T., et al. eds. Noise and Vibration Mitigation for Rail Transportation Systems, Notes on Numer-ical Fluid Mechanics and Multidisciplinary Design. Springer, Berlin Heidelberg, New York 118, 437–444 (2012) 24

Countermeasures of noise re-duction for Shinkansen electric-current collecting system and lower parts of cars

- K Murata
- T Sato
- K Sasaki

Murata, K., Sato, T., Sasaki, K.: Countermeasures of noise re-duction for Shinkansen electric-current collecting system and lower parts of cars. JR EAST Technical Review 1, 13–21 (2002)

Development of pantograph noise insulating panels

- Y Wakabayashi
- T Kurita
- M Horiuchi

Wakabayashi, Y., Kurita, T., Horiuchi, M.: Development of pantograph noise insulating panels. JR EAST Technical Re-view 12, 28–33 (2008)

The aerodynamic noise re-duction by porous materials and application to a current collec-tor

- T Sueki
- M Ikeda
- T Takaishi

Sueki, T., Ikeda, M., Takaishi, T.: The aerodynamic noise re-duction by porous materials and application to a current collec-tor. RTRI Report 22, 11–16 (2008)

On sound generated aerodynamically. I. Gen-eral theory Numerical solutions of acoustic propaga-tion problems using linearized Euler equations Towards a gen-eralized non-linear acoustics solver

- M J Lighthill
- C Bailly
- D Juve
- P 27 Batten
- E Ribaldone
- M Casella

Lighthill, M.J.: On sound generated aerodynamically. I. Gen-eral theory. Philosophical Transactions of the Royal Society of London. Series A 211, 564–587 (1952) 26 Bailly, C., Juve, D.: Numerical solutions of acoustic propaga-tion problems using linearized Euler equations. AIAA Journal 38, 22–29 (2000) 27 Batten, P., Ribaldone, E., Casella, M., et al.: Towards a gen-eralized non-linear acoustics solver. AIAA-2004-3001, 10th AIAA/CEAS Aeroacoustics Conference. Manchester, United Kingdom, May 10-12 (2004) 28

Numerical simulation on aero-dynamic noise of power collection equipment for high-speed trains

- F Yang
- B L Zheng
- P F He

Yang, F., Zheng, B.L., He, P.F.: Numerical simulation on aero-dynamic noise of power collection equipment for high-speed trains. Computer Aided Engineering 19, 44–47 (2010) (in Chi-nese)

The development of low noise pantograph. Foreign Locomotive and Rolling Stock Technology 5

- M Ikeda

Development of low noise pantograph adopted to the superexpress HAYATE. Mitsubishi Heavy Industries Technical Review 40

- K Shibata
- M Hirai
- T Hariyama

Noise evaluation of Shinkansen high-speed test train (FASTECH360S, Z)

- H Yamada
- Y Wakabayashi
- T Kurita