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The objective of this study was to investigate the effects of oblique tunnel portals on train and tunnel aerodynamics using a 1:20 scale moving model device. Transient pressure and micro-pressure waves were measured using pressure sensors as the train model travelled through various tunnel models at a speed of 350 km/h. The mitigation physical mechanism of oblique tunnel portal on the initial compression wave was explained. Experimental results showed that oblique tunnel portals had obvious mitigation effect on- the pressure gradient and micro-pressure wave induced by the train model passing through the tunnel model. A hat oblique tunnel portal combined with a buffer structure with top holes was particularly effective.

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... Various studies were conducted to investigate the non-uniform pressure acting on along-track infrastructures, such as tunnels, bridges, and subway station doors, during HSTs' passage [6,[14][15][16]. Carassale and Brunenghi [17] conducted experiments to investigate the displacement response due to the combined effects of train-caused pressure and vibration on a steel truss. ...

... To conduct a scaled moving-train experiment, a similarity criterion must be met. In our experiment, the experimental train speed is the same as actual train speed, which is common practice in moving model experiments [16,25]. As pointed out by the European code [38], the similarity criterion is met when the Reynolds number (Re) is greater than 3.6 9 10 5 and the scale ratio is higher than 1:25. ...

... As shown in Fig. 7, the pressure curve collected in the three tests are highly consistent with minor differences. The difference in the aerodynamic pressure of repetition tests is less than 2%, indicating the experiment system's high reliability [16]. ...

Three new types of acoustic insulation facilities, namely, full-enclosed (FEAB), bilateral-inverted-L-shaped (BILSAB), and inverted-L-shaped (ILSAB) acoustic barriers, are gradually receiving application along high-speed railways. A moving high-speed train (HST) may induce a nonlinear aerodynamic impact on the acoustic barrier. The HST may also experience a rapid change in its aerodynamic loads, reducing its stability and causing discomfort to passengers. Hence, nonlinear aerodynamic effects of three new types of high-speed railway acoustic insulation facilities when an HST passes by are compared based on model experiments and improved delayed detached eddy simulations (IDDES). Results show that: (i) When a HST runs at 350 km/h, the coefficient of pressure difference on the FEAB is 5.64 and 8.78 times higher than in the BILSAB and ILSAB, respectively. (ii) The amplitude of drag force coefficient of the head car when entering the FEAB is 2.80 and 2.95 times that of the BILSAB and ILSAB, respectively. The amplitude of lift coefficient of the tail car when running through the BILSAB is 1.27 and 1.37 times that of the FEAB and ILSAB. The amplitude of side force coefficient of the tail car when running through the ILSAB is 1.18 and 1.24 times that of the FEAB and BILSAB. (iii) For the tail car, the standard deviation of Cx when running inside the FEAB is 2.18 and 2.15 times that of the BILSAB and ILSAB, respectively. The standard deviation of Cy when running inside the FEAB is 1.42 and 1.51 times that of the BILSAB and ILSAB, respectively. The standard deviation of Cy when running inside the FEAB is 1.48 and 1.15 times that of the BILSAB and ILSAB, respectively. The results of this research may provide reference value for optimizing the structural patterns and improving the train’s operating stability.

... Accordingly, the variation of flow field inside the FENBRC may be similar to that inside the highspeed. Zhang et al. investigated the effect of different portal types on the transient pressure and micropressure wave when the train enters the tunnel through a 1:20 moving model experiment [30]. Another similar moving model experiment performed by Zhang et al. focused on the transient pressure caused by trains on the tunnel surface [31]. ...

... The moving-model experiment is conducted in the Key Laboratory of Track Traffic Safety in Central South University. The moving-model rig is 164 m long and can launch the train to 500 km/h [30]. Fig. 2 shows the power system of the movingmodel rig. ...

... When the HST arrives at the test section, the hook releases and the HST run with inertia. More detailed setups of this moving-model system were reported in [30]. ...

Two types of city-oriented noise barriers, i.e., fully-enclosed noise barrier and bilateral inverted L-shaped semi-enclosed noise barrier, have been gradually adopted in city centres along high-speed railways to reduce noise pollution. The aerodynamic impacts of high-speed trains present a threat to the long-term durability of the city-oriented noise barriers. To promote the usage and increase the sustainability of city-oriented noise barriers, a moving-model experiment system with city-oriented noise barriers and HST with a scale ratio of 1:16.8 is established. The train type is CRH380A and the train speed is up to 350 km/h. A systematic comparative study on the aerodynamic performance of the two types of city-oriented noise barriers is conducted. The similarities and differences of transient pressure time-histories, spatial distribution of pressure peaks and spectral characteristics of aerodynamic pressure acting on the two types of noise barriers are compared and discussed. Moreover, the influence of train speed on the characteristics of the train-induced aerodynamic pressure is also investigated. The results show that the pressure fluctuation of the two types of noise barriers is caused by different reasons. Compared with the fully-enclosed noise barrier, the transient pressure of the semi-enclosed noise barrier is more sensitive to train speeds. The research results may provide a reference for the engineering design of city-oriented noise barriers on high-speed railways.

... The distance of the two track is 250 mm and the distance between two Ibeams of a single track is 130 mm. Further details on the moving-model system can be found in a previous study (Zhang et al., 2017;Yang et al., 2022b,c). According to the European Standard (2013), the Reynolds number equivalence principle can be met when: (1) the scale ratio of the experiment is larger than 1:25; (2) the Reynolds number of the experiment is larger than 3.6 × 10 5 . ...

... Compared to a real CRH380B, some minor components, such as doors, windows, pantographs, and windscreen wipers are ignored in the HST model. Considering these components have limited influence on the aerodynamic performance of the train, the simplification can be accepted in the experiment (Zhang et al., 2017). The HST model has three carriages and is scaled at 1:16.8. ...

... The reason is the randomness of the highly turbulent slipstream generated during the HST operation. However, the pressure fluctuation laws of the three repeated tests are basically the same, and the maximum difference of the peak values is only 1.1% (less than 2%), indicating that the movingmodel device is stable and the experimental results are reliable (Du et al., 2020;Zhang et al., 2017). ...

The aerodynamic effect of a passing high-speed train (HST) may cause structural damage to the semi-enclosed noise barrier (SENB). Moreover, the rapid variation of the aerodynamic environment may deteriorate the operation stability of the train and passenger comfort. Three types of rectangular SENBs, namely, inverted-L-shaped noise barriers installed on double-line railways (ILSNB-DL), inverted-L-shaped noise barriers with a vertical board installed on double-line railways (ILSNBVB-DL) and inverted-L-shaped noise barriers with a vertical board installed on single-line railways (ILSNBVB-SL), are considered in this research. By establishing a 1:16.8 train–SENB moving-model system and a corresponding large eddy simulation (LES) model, the time-history and spatial characteristics, flow field mechanism and spectral characteristics of the aerodynamic pressure acting on the three types of SENBs are investigated. Moreover, the differences in the time-history characteristic, flow field mechanism and spectral characteristic of the aerodynamic loads on the HST when passing through the three types of SENBs are also compared. The aerodynamic pressure inside ILSNBVB-DL is more than 27% higher than that of ILSNB-DL, and the aerodynamic pressure inside ILSNBVB-SL is more than 16% higher than that of ILSNBVB-DL. When the HST enters and exits ILSNBVB-SL, the area with positive and negative pressure on the train surface varies the most dramatically, causing the amplitude of the lift force of the HST when passing through ILSNBVB-SL being approximately four times the value when the HST passes through ILSNB-DL and ILSNBVB-DL. When the HST enters and exits ILSNB-DL and ILSNBVB-DL, the pressure difference between the two sides of the HST is greater than that when the HST enters and exits ILSNBVB-SL, leading to the maximum amplitude of the side force of the HST passing through ILSNB-DL being 1.8 times of the value for ILSNBVB-DL and ILSNBVB-SL.

... In addition, a brake box is also set up to prevent the train from running out of the test line when the braking system fails. More detailed information about the moving model rig can be found in the reference (Zhang et al., 2017). ...

... However, according to the CEN European standard (2013), when the model scale ratio is greater than the critical scale ratio of 1:25, the influence of the Reynolds number on the flow field can be minimised. Moreover, if the Reynolds number of the moving model test is larger than the critical Reynolds number, that is, Re > 3.6 × 10 5 , the flow field can approximately meet the similarity criterion (Zhang et al., 2017). When the scale ratio and the Reynolds number of the moving model test are larger than the critical scale ratio and the critical Reynolds number, respectively, the Reynolds number barely influences the aerodynamic characteristic of the train (Bell et al., 2014). ...

... The scale ratio of the moving model test evidently meets the requirement of the critical scale ratio. The Reynolds number is usually calculated on the basis of the characteristic height according to previous studies (Niu et al., 2016;Yang et al., 2016;Zhang et al., 2017;Zhou et al., 2014). Thus, H' = 0.23 m in this research. ...

With the increasing speed of high-speed trains, the aerodynamic impact of trains on high-speed railway noise barriers has gradually become a focus of attention. Compared with traditional vertical noise barriers, the bilateral inverted-L-shaped noise barrier (BILSNB) has better noise insulation performance, but its aerodynamic impact may be more prominent. In this research, a moving train-BILSNB test system with a scale ratio of 1:16.8 is established, and the influence of train speed and the opening width on the aerodynamic pressure is analysed and discussed. The large eddy simulation is applied to investigate the influence mechanism of flow field on the aerodynamic performance of the BILSNB. The main conclusions are as follows. (1) The pressure amplitude caused by the passing of the train head is 36.67% greater than that generated by the passing of the train tail on average. (2) The maximum pressure of the BILSNB appears at the bottom area. When the height of the measuring point increases from 0.5H to 1.6H, the pressure coefficient of peak positive pressure, peak negative pressure and pressure amplitude decrease by 29.0%, 17.0% and 15.5%, respectively. (3) The aerodynamic pressure in the BILSNB has a longitudinal end effect: the pressure coefficient of positive peak pressure and pressure amplitude at the inlet section are 27.6% and 17.5% higher than the corresponding average value of all middle sections, respectively. (4) The pressure amplitude of the BILSNB is approximately proportional to 2.15 power of the train speed. The pressure coefficient of the BILSNB is approximately a power function of the opening width, and the value range of the index is about (−0.26, −0.30). (5) The mechanism of the longitudinal end effect is as follows: When the train arrives at the inlet section, the high-speed airflow in front of the train head cannot flow around in time resulting in the impact effect of the airflow on the inlet section becomes greater than that on the middle section. The influence mechanism of the opening width is as follows: The narrower the opening width is, the more intense the airflow inside the BILSNB is compressed, and the impact effect of the airflow on the noise barrier is more significant.

... Miyachi et al. (2014) conducted a set of model experiments to explore the pressure wave when the train runs through the branch tunnel and the pulse waves radiated from the portals of the main tunnel to the branch. Zhang et al. (2017b) investigated the influence of different oblique tunnel portals on the train and tunnel aerodynamics by using a 1:20 scaled moving model. Besides, investigation regarding the effect of vented tunnel portal (Heine et al., 2018), tunnel portal geometry (Howe et al., 2000), and localized high temperature (Wang et al., 2020b) on pressure waves were also carried out. ...

... In this section, numerical model was established based on the method described before. Initial parameters are the same with the motion model test carried out by Zhang et al. (2017b). As shown in Fig. 8, simulation results of the transient pressure curves at the monitoring point T7 (in the middle of the model tunnel) and the micro pressure wave at tunnel exit were compared with experimental measurements., presenting good agreement. ...

... The comparison shows very good agreement with experimental results, which confirms the simulated values being accurate and reliable. (Zhang et al., 2017b). ...

Transient pressure induced by the trains passing through tunnels has a significant influence on tunnel structural safety. When tunnels are constructed at somewhere with high altitude and low atmospheric pressure the impact of ambient pressure cannot be ignored. In the current study, a three-dimensional, unsteady, compressible, RNG ᴋ–ε turbulence model, and the dynamic mesh was employed to explore the effect of ambient pressure on the propagation characteristics of pressure waves inside the tunnel when the train passes through the tunnel at the same speed (100 km/h). Results show that (1) The ambient pressure has limited influence on the waveform of the pressure but strongly affects the peak value of pressure wave, where positive peak value P-max and peak-to-peak pressure difference ΔP linearly increase and negative peak value P-min proportionally decreases with the increase of ambient pressures; (2) The initial compression wave ΔPN and pressure increase caused by the friction effect ΔPfr linearly increase as ambient pressures increases. However, the ratio of ΔPN to P-max is not sensitive to the ambient pressure and values of ΔPNP-max remains to be constant.

... To date, many scholars research have conducted investigation concerning the aerodynamic pressure characteristics caused by the high-speed trains (This specifically refers to the high-speed railway system, not the urban rail transit system) by using theoretical analysis (Hara, 1965;Woods and Pope, 1976), field measurement (Iida et al., 2001), moving-model experiment (Gilbert et al., 2013;Zhang et al., 2017c), and numerical simulation (Niu et al., 2018b;Ricco et al., 2007). They mainly focus on the characteristics of pressure waves induced by highspeed trains passing through tunnels and the influence of various factors (Niu et al., 2020). ...

... Gilbert et al. (Gilbert et al., 2013) investigated the transient aerodynamic pressure around high-speed trains when the train travels from unconfined space to the confined spaces, with highlight on the pressure variation at entry moment. Zhang et al. (Zhang et al., 2017c) studied the impact of different inclined tunnel portals on the aerodynamics of trains and tunnels by using a 1:20 scaled moving model. Measurements show that the inclined opening reduces the pressure gradients and micro pressure waves, especially when the tunnel is designed with a buffer structure with top vents. ...

... The magnitude of the fluctuation of lift and the drag forces gradually decreases as the length of train tapered nose increases. Other influencing factors like tunnel portal geometry (Howe et al., 2000;Zhang et al., 2017c), tunnel cross-section (Lu et al., 2020;Wang et al., 2018), crosswind at the tunnel entrance , ambient wind (Chen et al., 2017), and localized high temperature (Wang et al., 2020b) are also addressed by some other researchers. ...

The continuous construction of extra-long metro tunnels and the shortened departure intervals enable double trains to simultaneously drive in the same tunnel direction to be possible. Transient pressure changes induced by trains passing through tunnels have a remarkable influence on the structural safety of tunnels. In this study, pressure waves generated by single and double trains passing through the tunnel are both explored by numerical simulation. The accuracy and feasibility of the simulation method of double train tracking operation is verified by comparison with the small-scale experimental research. Based on the verified simulation method, the pressure wave and its propagation characteristics in the aforementioned two situations are investigated. Variation of transient pressure on the surface of the train and tunnel are compared and analyzed. Results show no obvious difference on the generation and propagation mechanism of pressure waves between the two typical situations. However, the propagation of the pressure wave is found to be more complicated in the double train tracking mode. More concretely, in the double train tracking mode, the maximum transient pressure P-max, minimum transient pressure P-min, and the peak-to-peak value of transient pressure ΔP on the first train surface are observed to be same as those in the single train condition, whereas those of the second train denote different values. The transient pressure at different positions in the tunnel and the waveform after the second train entering the tunnel are different compared to that in the single train condition, while the peak value exhibits insignificant difference. Moreover, the maximum pressure, minimum pressure, and maximum peak-to-peak pressure occur inside tunnel denote no obvious difference in the two typical scenarios.

... Murray's theoretical research on the tunnel entrance hoods show that the installation of the tunnel hoods will increase the rise time of the initial compression wave, thereby decreasing the pressure gradient [18]. Studies nowadays have contributed extensively to designing optimized tunnel hoods to reduce the amplitude of MPW at the tunnel exit [19][20][21][22][23]. Although related studies have been performed on the infuences of tunnel hoods, limited investigations have been conducted on the efects of MPW behaviors of the linings. ...

... Te evaluation standard of MPW at the tunnel exit of a high-speed railway is that the amplitude values of MPW at 20 m and 50 m away from the tunnel exit are less than 50 Pa and 20 Pa, respectively [22]. ...

When the tunnel has damages such as deformation and cracking, the lining structure should be set to reinforce the tunnel. In this study, a three-dimensional numerical method is performed to study the aerodynamic effects caused by the train passing through a tunnel with segmented linings at 350 km/h. The influence of the numbers, thickness, location, and types of the segmented lining structure on MPW is analyzed. The results show that the segmented linings located at the middle of the tunnel have a better mitigation effect on MPW than that of the normal linings, which increases with the segment number and the thickness of the linings. When the damage occurs near the entrance of the tunnel, a segmented lining structure with a constricted section slightly away from the tunnel entrance can be used to reduce its adverse effect on MPW.

... They found that when the slope of the portal was 1:1.75, the peak value of the change gradient of the micro-pressure wave decreased by approximately 10.8%. The team also compared the differences in micropressure waves among different tunnel portal types by using a moving train model and found that the hat oblique type of a tunnel portal seemed to be the best choice for reducing the micro-pressure wave peak and pressure gradient (Zhang et al., 2017). Obviously, the aerodynamic effect of the relative motion between the tunnel portal and HST is considerable in the absence of crosswind. ...

... The distance between the end part near the wind tunnel wall and the wind tunnel wall was 1 m reducing the influence of the pressure relief caused by the opening of the wind tunnel wall on the flow field mode in the tunnel. A detachable hat oblique type tunnel portal (Zhang et al., 2017) was 1.17 m long, had a diagonal angle of 30 • , and was installed in tunnel A or tunnel B depending on the selected test condition. The bridge model was located in the middle of the two tunnels, whose length and width were 4 and 1.29 m, respectively. ...

The moving train model test for wind tunnels is an advanced and effective research method for studying the aerodynamic effect of trains passing through tunnel portals in crosswind environments. However, the modelling of tunnel portal structures is cumbersome, and its influence on test results remains unclear. Here, the influence law of the presence and absence of a tunnel portal on the aerodynamic performance of a train was investigated via a wind tunnel test and an improved delayed eddy simulation turbulence model with “mosaic” mesh technology. First, the difference between train locomotion on the windward and leeward side lines with and without a portal was compared from the perspectives of aerodynamic load amplitude, power spectral density (PSD), and standard deviation. Second, the influence of vehicle speed on the amplitude of the train’s aerodynamic load was studied, and the recommended critical speed was determined. Finally, the applicability of the moving model test results under different scale ratios (Reynolds numbers) was explored. Key results show that the aerodynamic load amplitude, PSD peak and standard deviation of the train on the leeward side line are generally higher than those on the windward side line. As indicated by the lift force in the ‘EX’ process without the tunnel portal, the amplitude on the leeward side line is 1.73 time the corresponding values on the windward side line. At speeds of 6, 12 and 18 m/s, when the moving train model speed reaches 12 m/s, the influence of the tunnel portal on the aerodynamic load amplitude can be ignored. The results imply a serious distortion of the aerodynamic load amplitude for the 1:20 model scale, whereas it appears to be appropriate at the 1:16.8 and 1:10 scales. The model test with a Reynolds number of 2.67 × 105 offers an ideal reference value for real trains.

... The maximum launch speed of the train models on the test line is 500 km/h. Many model test studies have been conducted on the test bed (Du et al., 2020;Liu et al., 2019;Meng et al., 2019;Zhang et al., 2017Zhang et al., , 2019, and the model test device has been introduced in detail in previous studies. ...

... Dynamic similarity can be expressed by a similarity criterion, but it is almost impossible to satisfy all similarity criteria at the same time in a model test, so usually only the similarity criterion that plays a major role in the flow process is considered. For the flow around the train, the Reynolds similarity criterion is mainly considered (Du et al., 2020;Zhang et al., 2017). The CEN European Standard (2009) clearly states that the train aerodynamic characteristics can be effectively assessed by a scaled moving model test and that, when the Reynolds number exceeds 2.5 × 10 5 , the flow field of the model test can be approximately considered to meet the Reynolds similarity criteria. ...

Transient pressure variations on train and platform screen door (PSD) surfaces when a high-speed train passed through an underground station and adjoining tunnel were studied using a moving model test device based on the eight-car formation train model. The propagation characteristics of the pressure wave that was induced when the train passed through the station and tunnel at a high speed were discussed, and the effects of the train speed and station ventilation shaft position on the surface pressure distribution of the train and PSDs were analyzed and compared. The results showed that the pressure fluctuation law is different for the train and PSD surfaces, and the peak pressure increases significantly with an increase in the train speed. Ventilation shafts changed the pressure waveform on the surface of the train and PSDs and greatly reduced the peak pressure. A single shaft at the rear end of the platform and a double shaft at the station had the most significant effect on relieving transient pressure on the surface of the train and PSDs, respectively. Compared with the case with no shaft, these two shafts reduced the maximum amplitude pressure variation of the train and PSD surfaces by 46.3% and 67.4%, respectively.

... Bazı bilim adamları, tünel girişinde cihazlar kurarak bir tüneldeki basınç dalgasını veya tünel çıkışındaki mikro basınç dalgasını azaltmayı başarmışlardır. Bu çalışmalardan Zhang vd., [23] tarafından yapılan çalışmalar Şekil 5'de gösterilmektedir. ...

... Şekil 5. Tünel portal modelleri: (a) duvar tip, (b) halka şekilli ve eğik yapılı, (c) şapka şekilli ve eğik yapılı, (d) üstü çift delikli düz şekilli (e) birleşik şapka eğik yapı[23] Pencereli bir flüt yapısı için ilk sıkışma dalgası ve mikro basınç dalgası üzerindeki etkisi Howe[24,43,44,45] tarafından incelenmiştir. Pencerelerin konum, sayı ve boyutlarının etkilerine ilişkin analizler detaylı olarak yapılmış; önerilen bazı değerler ve formüller ortaya konmuştur. ...

Yüksek standartlı demiryolları, kat ettiği mesafeler ve içerdiği karmaşık mühendislik yapıları açısından oldukça zorlu imalatlardır. Gerek imalat gerekse işletmecilik faaliyetleri sırasında maliyet etkin olması istenir. Güzergâh çalışmalarından mühendislik yapılarının tasarımına kadar bu durumu etkileyen birçok parametre vardır. Bu çalışmada, yüksek hızlı demiryollarında tünel tasarımı konusuna odaklanmaktadır. Bu amaçla öncelikle yüksek hızlı demiryolu tünel tasarımında kullanılan ana hat ve tünel güvenliği konuları uluslararası standartlar çerçevesinde irdelenmiş, bu konuda dünyada yapılan son çalışmalar derlenmiştir. Ardından Türkiye’de geçmişi yaklaşık 20 yılı bulan yüksek hızlı demiryolu tünel imalat tecrübeleri aktarılmıştır. İlk tasarımından bu yana neredeyse hiç değişmeyen tünel yapısında, işletme sırasında oluşan sorunlar çerçevesinde yapısal ve geometrik iyileştirmeler gerektiği sonucuna varılarak bu kapsamda öneriler sunulmuştur.

... Current mitigation strategies encompass installing a hood at the tunnel entrance to lower the initial wavefront gradient, 11,12 alleviating the nonlinear steepening of the wavefront within the tunnel, 13,14 and deploying mufflers at the tunnel's exit. 15,16 Various types of hoods at the tunnel entrance, including flared hoods, 17 oblique hoods, 18 hoods with expanded cross sections, 6 and windowed hoods, 19 have undergone extensive research to mitigate the initial wavefront gradient. Saito et al. 6 proposed an improved two-step hood, which involves removing the vertical connection between the first and second hoods and extending the first hood, to better reduce the MPW radiation. ...

The micro-pressure waves (MPW) released from maglev tunnel portals can generate audible sonic booms and cause structural resonance in surrounding buildings, posing challenges to developing high-speed maglev trains. This paper proposes a novel porous media hood (PMH) and investigates its mechanism for mitigating the sonic booms emitted from tunnels. The numerical model employs the improved delayed detached eddy simulation turbulence model and overset grid technology, validated against data from moving-model experiments. The influences of the PMH's inherent properties and geometric parameters on MPW, flow field evolution, and aerodynamic loads on the train body were comprehensively discussed. The research demonstrates that PMH effectively dampens the initial wavefront gradient at the entrance and reduces the MPW amplitude by intensifying radiation within its exit vicinity. The porosity of 0.2 facilitates a seamless transition for the streamlined head from the ventilated PMH to the airtight tunnel. Lengthening the PMH enhances its MPW mitigation effect, whereas the impact of PMH thickness is minor. The PMH effectively diminishes the reflection intensity of compression and expansion waves at the tunnel ends, leading to a reduction in the magnitude and changing rate of train aerodynamic loads. This underscores the PMH's potential to enhance passengers' auditory comfort and alleviate issues related to train sway.

... Based on moving model experiments, scholars have studied the traincaused aerodynamic pressure impact on infrastructure such as overpass bridges (Liang et al., 2020), sound barriers (Deng et al., 2020;Liu et al., 2023b;Yang et al., 2022a), tunnel walls , tunnel auxiliary facilities , and train platforms (Zeng et al., 2021;Zhou et al., 2014). They have also investigated the characteristics micro-pressure wave generated from trains going out tunnel out and the effects of portal shape (Zhang et al., 2017(Zhang et al., , 2019, as well as the spatiotemporal characteristics of airflow generated by train motion (Soper et al., 2014;Zampieri et al., 2020) and smoke diffusion in tunnels under slipstream conditions . Based on on-site testing, scholars have tested the wind speed distribution characteristics generated from train movement in open-air (Rocchi et al., 2018), the characteristics of aerodynamic pressure on sound barriers when trains pass by (Soper et al., 2019;Xiong et al., 2018Xiong et al., , 2020, the aerodynamic characteristics of freight trains (Quazi et al., 2021), the micro-pressure wave buffering effect of tunnel buffer structures (Okubo et al., 2022), and passenger pressure comfort when trains run through tunnels (Liu et al., 2017). ...

The detached tunnel lining concrete blocks poses a serious threat to the safety of moving high-speed train. Understanding the flight characteristics of detached blocks from the tunnel soffit under train piston airflow is essential for devising appropriate measures to mitigate such risks during train operation. Computational Fluid Dynamics (CFD) simulation methods, known for their high efficiency and good repeatability, are effective approaches to study this subject. Large Eddy Simulation (LES), Improved Delayed Detached Eddy Simulation (IDDES), and Unsteady Reynolds-Averaged Navier-Stokes (URANS) are three commonly used turbulence simulation methods in the CFD simulation of train/tunnel aerodynamics. In this study, a three-dimensional CFD simulation model based on the three turbulence simulation methods is established for the airflow-tunnel-train-detached block system, and an experiment is conducted for validating the CFD model. Using the established models, the influence of different turbulence simulation methods on the flight trajectory and aerodynamic coefficients of detached lining blocks under train-induced airflows is compared. By visualizing the macroscopic flow field inside the tunnel and the local flow field near the detached block, the flow mechanisms of detached blocks under different turbulence simulation method conditions are revealed. The results showed that in the 1st stage (BTT stage), the flight of the detached block is influenced by the airflow near the train body, while in the 2nd stage (ATT stage), it is mainly affected by the train wake vortex. Compared with experimental results, the errors of LES and IDDES in simulating the longitudinal direction displacement of the block are only 2.3 % and 5.5 %, respectively, while the error of URANS is 10.6 %. The simulation error of URANS for the longitudinal direction flight speed reached 8.8 % in the ATT stage. In the BTT stage, LES and IDDES predicates more and larger leeward side vortex structures of the detached block, while URANS predicates fewer and smaller vortex structures. Compared with URANS method, the dissipation rate of the vortex structures simulated by LES and IDDES in the ATT stage is slower. These are the main reasons explaining why the flight characteristics of detached lining blocks obtained by URANS method are different from the LES and IDDES methods.

... Several scholars have also used model test methods to study the safety of operating trains relative to the surrounding flow field. Zhang et al. 17 studied the effects of inclined tunnel entrances on the aerodynamics of trains and tunnels and revealed the physical mechanism through which inclined tunnel entrances slow initial compression waves. Niu et al. 18 studied the effect of the Reynolds number on the aerodynamic force and pressure of trains at yaw angles of 0° and 15° and analyzed the difference in the Reynolds number effect between the front and rear trains. ...

Given the influence of air intake from inclined shafts in existing tunnel ventilation systems on train comfort and aerodynamic safety, a numerical analysis method is used to study the comfort and aerodynamic safety of operating trains under three conditions—inclined shaft closed and inclined shaft open without and with air intake—and to explore the variation law of transient pressure and aerodynamic force (lift coefficient, transverse force coefficient, and overturning moment coefficient). Combined with practical engineering and requirements, the influence of inclined shaft air intake on train operation comfort and aerodynamic safety is analyzed. Through this research, the influence of using air intake from the inclined shaft of an existing tunnel, a ventilation scheme of the new Wushaoling Tunnel, on the comfort and aerodynamic force of trains is revealed, and the comfort and aerodynamic safety of trains in an actual project are evaluated, verifying the rationality of the ventilation scheme of the Wushaoling Tunnel.

... Researchers have conducted a series of studies against harmful influences of train-induced aerodynamic pressure, including the micro-pressure wave at tunnel entrance , dynamic response of the train , and fatigue performance of the train . For example, Zhang et al. (2017) conducted dynamic model experiments to study the micropressure waves generated by high-speed trains while passing through the tunnels of five different portals. They found that the oblique portals have a noticeable alleviating effect on the micro-pressure waves. ...

High-speed railway tunnels in various countries have continuously reported accidents of vault falling concrete blocks. Once the concrete block falling occurs, serious consequences follow, and traffic safety may be endangered. The aerodynamic shockwave evolves from the initial compression wave may be an important inducement causing the tunnel lining cracks to grow and form falling concrete blocks. A joint calculation framework is established based on ANSYS Fluent, ABAQUS, and FRANC3D for calculating the crack tip field under the aerodynamic shockwave. The intensification effect of aerodynamic shockwaves in the crack is revealed, and the evolution characteristics of the crack tip field and the influence factors of stress intensity factor (SIF) are analyzed. Results show that (1) the aerodynamic shockwave intensifies after entering the crack, resulting in more significant pressure in the crack than the input pressure. The maximum pressure of the inclined and longitudinal cracks is higher than the corresponding values of the circumferential crack, respectively. (2) The maximum SIF of the circumferential, inclined, and longitudinal crack appears at 0.5, 0.68, and 0.78 times the crack front length. The maximum SIF of the circumferential crack is higher than that of the inclined and longitudinal crack. The possibility of crack growth of the circumferential crack is the highest under aerodynamic shockwaves. (3) The influence of train speed on the SIF of the circumferential crack is more than 40%. When the train speed, crack depth, and crack length change, the change of pressure in the crack is the direct cause of the change of SIF.

... The above studies analyzed the amplitude and waveform of MPW from the perspective of temporal pressure. However, current MPW evaluation standards include the impulse amplitude and the acoustic evaluation 11,26 (as summarized in Fig. 1). For example, the impulse amplitude in Japan, South Korea, and China adopts a single point MPW amplitude as the threshold. ...

The propagation of the weak shock wave (WSW) to the tunnel exits and their radiation as micro-pressure waves (MPWs) may cause sonic booms or structural resonance of buildings, posing potential hazards to humans, animals, and buildings in the exit's environment. The characteristics of the WSW and sonic booms of a maglev train/tube coupling model were studied based on the two-dimensional axisymmetric unsteady Reynolds average Navier–Stokes turbulence model. In the later stage of a MPW, the formation mechanism, geometry, and kinematic characteristics of compressible vortex rings (CVRs) were systematically analyzed. The inertial effect causes the initial wavefront to gradually transition from a Gaussian-shape waveform to a triangular waveform during its propagation, eventually coalescing into a WSW. The overpressure, density jump, and shock Mach number at the WSW location all increase with the increasing train speed, while the WSW thickness decreases accordingly. The formation distance of the WSW is inversely proportional to the amplitude of the initial wavefront gradient, and the WSW directly causes the occurrence of the exit sonic boom. The MPW amplitude has significant directionality with a largest value in the axial direction. Within the speed range of 450–700 km/h, the sound pressure level of the MPW exceeds the hearing threshold and even reaches the feeling threshold. The evolution of CVRs includes primary CVR, secondary CVR, and Kelvin–Helmholtz vortices. Primary CVR has the greatest impact on the axial MPW among them. The occurrence of CVRs will cause a second small noise level other than the sonic boom.

... Fukuda [7] investigated the effect of the cross-section area of hoods using axisymmetric models; they found that a hood with multi-step cross-sections is more effective than those with a constant cross-section. Zhang [8][9][10] studied the effects of different tunnel portals on tunnel aerodynamics using a moving model test; the results indicated that the hat oblique portal combined with a buffer structure with top holes is particularly effective. Auvity [11] revealed that opening holes on the hood can delay the rising time of the compression wave further by splitting the wavefront into multiple stages. ...

The MPW that emits from a tunnel’s exit when a high-speed train passes through is a serious environmental problem which increases rapidly with the speed of the train. To alleviate the MPW problem at 400 km/h, the aerodynamic effects caused by the hood located at the entrance or exit of a tunnel are studied by numerical method, and the influences of hood geometry, such as an enlarged cross-section, oblique entrance, and opening holes on the MPW, are also investigated. The research indicates that the enlarged cross-section of the hood at the entrance and exit of the tunnel has opposite effects on the MPW, and the oblique section can alleviate the MPW by extending the rising time of the compression wave and increasing the spatial angle at the hood exit. The pressure gradient can be mitigated through delaying the rising of the compression wave by opening holes on the side wall of the hood, and the relief effects of the holes can reduce the MPW further. The MPW problem when a train passes through a tunnel at 400 km/h can be effectively alleviated by an optimized oblique enlarged hood with opening holes, even up to train speeds of 500 km/h.

... Furthermore, the combination of ventilation windows with the hat oblique buffer hood has been extensively studied by various scholars. Zhang et al. 18,19 investigated the optimization of aperture rates for the aerodynamic buffering performance of a hat oblique buffer hood using numerical simulations and moving model experiments. Their findings revealed that an optimized ventilation window configuration led to a reduction of 50.22% in the peak of the pressure gradient (P PG ) and 51.22% in the P MPW in comparison with scenarios without a buffer hood. ...

As high-speed trains exceed 400 km/h, tunnel aerodynamics pose significant challenges. The hat oblique tunnel buffer hood with enlarged cross section and ventilation windows (HEW) is a promising solution to mitigate micro-pressure waves (MPWs). However, there is limited research on HEW ventilation window configurations. Thus, field measurements and numerical simulations were conducted using the slip grid technique and an improved delayed eddy simulation turbulence model, with validation against field data. The study investigated the effects of aperture rate and ventilation window arrangement, analyzing the initial compression wave, pressure gradient, MPW, and flow field in the tunnel buffer hood under various ventilation window setups. Findings emphasize that increasing the aperture rate or placing ventilation windows near the tunnel entrance reduces MPWs when a high-speed train enters the buffer hood. However, it intensifies MPWs when the train transitions from the buffer hood to the tunnel. Optimal MPW mitigation is achieved with approximately 15% aperture rate and a ventilation window distance from the slope end of 0.3–0.4 times the enlarged cross section length. Double ventilation windows outperform single or three windows in MPW reduction, with longitudinally arranged windows at the top facilitating more efficient high-pressure air escape compared to circumferential windows.

... Therefore, several studies focus on the characteristics of the ICW and corresponding mitigation measures. Zhang et al. (2017) conducted scaled model tests and found that combining buffer structures with a hat oblique tunnel portal effectively mitigates the MPW. Zhang et al. (2018) quantitatively established a linear relationship between the ICW and the MPW. ...

Purpose
This study aims to propose a series of numerical and surrogate models to investigate the aerodynamic pressure inside cracks in high-speed railway tunnel linings and to predict the stress intensity factors (SIFs) at the crack tip.
Design/methodology/approach
A computational fluid dynamics (CFD) model is used to calculate the aerodynamic pressure exerted on two cracked surfaces. The simulation uses the viscous unsteady κ-ε turbulence model. Using this CFD model, the spatial and temporal distribution of aerodynamic pressure inside longitudinal, oblique and circumferential cracks are analyzed. The mechanism behind the pressure variation in tunnel lining cracks is revealed by the air density field. Furthermore, a response surface model (RSM) is proposed to predict the maximum SIF at the crack tip of circumferential cracks and analyze its influential parameters.
Findings
The initial compression wave amplifies and oscillates in cracks in tunnel linings, resulting from an increase in air density at the crack front. The maximum pressure in the circumferential crack is 2.27 and 1.76 times higher than that in the longitudinal and oblique cracks, respectively. The RSM accurately predicts the SIF at the crack tip of circumferential cracks. The SIF at the crack tip is most affected by variations in train velocities, followed by the depth and length of the cracks.
Originality/value
The mechanism behind the variation of aerodynamic pressure in tunnel lining cracks is revealed. In addition, a reliable surrogate model is proposed to predict the mechanical response of the crack tip under aerodynamic pressures.

... In academic and engineering circles, the adverse impacts of aerodynamic pressures caused by HSTs have been extensively followed with interest. On the one hand, when ICW propagates to the tunnel exit, the micro-pressure wave produces noises and vibrations to residential buildings near the tunnel exit Zhang et al., 2017;Zhang et al., 2019). On the other hand, the strong aerodynamic pressure can transmit into the carriage from the train gaps, resulting in discomfort to passengers. ...

Falling concrete blocks are serious problems in high-speed railway tunnels, and they cause delays of high-speed trains (HSTs) and even compromise driving safety. When HST-induced aerodynamic shockwaves propagate into cracks, the intensified pressure makes the cracks grow and connect, resulting in falling concrete blocks. In this study, the longitudinal, oblique and circumferential cracks at the tunnel vault are selected as representatives. The temporal, spatial and spectral characteristics of the aerodynamic pressure in the cracks are studied using the unsteady viscous k-ε turbulence model. The aerodynamic intensification effect in the lining crack is also revealed. Results show that the maximum pressure of the circumferential crack is 1.51 and 1.37 times that of the longitudinal and oblique cracks, respectively. On the basis of the results of soil–tunnel–crack models established in ABAQUS, two response surface models (RSMs) are established to quantify the effects of important factors, including crack length, crack depth, crack width, incident angle of the aerodynamic shockwave and train velocity, on the maximum tensile strain of the crack tip of circumferential cracks. Train velocity exerts the greatest influence on the maximum tensile strain in the circumferential crack, followed by crack width. Moreover, a field measurement is performed to investigate the dynamic strain of crack tips under train-induced aerodynamic loads and verify the proposed RSM. The maximum tensile strain caused by aerodynamic pressure is approximately 0.31–0.86 times of the maximum tensile strain of concrete. The proposed RSM can realise a reasonable prediction of the dynamic strain of crack tips. This research may be valuable for analysing the crack tip stability of tunnel lining cracks and guaranteeing the structural health of high-speed railway tunnels.

... 9,10 For example, Baron et al. 11 introduced the classical linear acoustic formulation to predict the MPW. Zhang et al. 12 conducted moving model tests to compare the mitigation performance of five types of tunnel portals on the MPW. Okubo et al. 13,14 carried out field experiments to investigate the alleviation effect of bench shafts and tunnel hoods with windows on the MPW. ...

Spalling of concrete blocks from tunnel linings is a severe defect in high-speed railway tunnels (HSRTs). The amplified initial compression wave (ICW) in circumferential cracks induced by high-speed trains may be the main cause of crack propagation and concrete block formation. To investigate the aerodynamic amplification effect of the ICW in circumferential cracks, tunnel-crack models are established and solved based on the unsteady viscous k–ε turbulence method. A scaled indoor experiment is carried out to verify the reliability of the calculation method. The characteristics of amplified pressure and corresponding mechanisms are analyzed and revealed. Three influential parameters, including the crack width, crack depth, and train velocity, are analyzed and discussed in detail. The main conclusions are as follows: (1) the maximum amplified pressure in a typical circumferential crack is 5.68 times that of the ICW. (2) The maximum power spectrum density (PSD) of the aerodynamic pressure at the crack tip is 91.04 times that at the crack mouth. The crack tip suffers most from the aerodynamic impact of the fluctuating component of pressure waves, whereas the crack mouth is most susceptible to the average component. (3) The train velocity is the most influential parameter on the maximum pressure at the crack tip, followed by the crack depth. The power function with an exponent of 2.3087 is applicable for evaluating the relationship between the maximum pressure and train velocities. (4) The train velocity and crack depth are most influential parameters to the maximum PSD. The relationship between the maximum PSD and the crack widths, crack depths, and train velocities can be reasonably described by the power function. (5) The mechanism of pressure amplification is as follows: first, the superposition of the internal energy possessed by air molecules near crack surfaces. Second, the increase in the internal energy of air near the crack tip because of the gradually narrowing space. The results of our research may be applicable in analyzing the cracking behavior of tunnel lining cracks and preventing the spalling of concrete blocks in HSRTs.

... The time step was set to 0.0119 s. 50 iterations were made in each time step to ensure that appropriate residuals were obtained, and the convergence criteria of all variable residuals were set at 10 −4 [5,11,31]. The numerical calculation data were output by the user-defined function (UDF) in ANSYS FLUENT. ...

When constructing a long undersea tunnel, cross-sectional area of some parts of the tunnel will be changed to strengthen the tunnel or save construction costs, which will cause a change in aerodynamic characteristics of the tunnel. By comparing variable cross-section(VCS) tunnel and constant cross-section (CCS) tunnel, the influence of abrupt cross-section on pressure transients and slipstream in the long tunnel was studied. The RNG k-ε turbulence model was adopted for numerical simulation, which was validated by the moving model test. The results show that the closer it to the abrupt cross-section, the larger the difference between the positive peak pressure of the VCS tunnel and that of the CCS tunnel, reaching a maximum of 7.63% at 5.43 km. The difference in slipstream velocity in the longitudinal direction between the two tunnels can reach 18.7% at most, but it is almost the same in the other two directions. In addition, the impact of the abrupt section on slipstream in different areas of the tunnel is different. This research has an important reference value for parameter design of long variable cross-section tunnel and layout of auxiliary facilities in tunnel.

... By comparing the before and after results, they proved that Helmholtz resonators in tunnels of different lengths can effectively reduce the micro-pressure wave amplitude. Zhang et al. [6,7] observed in their study that the initial increase in pressure at all measurement points at the tunnel exit was mainly determined by the initial compression wave generated at the time of train entry. Using a 1:20 dynamic model test rig, they measured the transient pressure and micro-pressure waves of a 350-km/h train model passing through various tunnel models and observed that the combination of a buffer structure with a roof hole and a cap-shaped diagonal cut tunnel opening can effectively reduce the micropressure wave amplitude. ...

A 600-km/h maglev train can effectively close the speed gap between civil aviation and rail-based trains, thereby alleviating the conflict between the existing demand and actual capacity. However, the hazards caused by the micro-pressure wave amplitude of the tunnel that occurs when the train is running at higher speeds are also unacceptable. At this stage, mitigation measures to control the amplitude of micro-pressure waves generated by maglev trains at 600 km/h within reasonable limits are urgent to develop new mitigation measures. In this study, a three-dimensional, compressible, unsteady SST K–ω equation turbulence model, and an overlapping grid technique were used to investigate the mechanism and mitigation effect of Helmholtz resonators with different arrangement schemes on the micro-pressure wave amplitude at a tunnel exit in conjunction with a 600-km/h maglev train dynamic model test. The results of the study showed that a pressure wave forms when the train enters the tunnel and passes through the Helmholtz resonator. This in turn leads to resonance of air column at its neck, which causes pressure wave energy dissipation as the incident wave frequency is in the resonator band. This suppresses the rise of the initial compressional wave gradient, resulting in an effective reduction in the micro-pressure wave amplitude at the tunnel exit. Compared to conventional tunnels, the Helmholtz resonator scheme with a 94-cavity new tunnel resulted in a 31.87% reduction in the micro-pressure wave amplitude at 20 m from the tunnel exit but a 16.69% increase in the maximum pressure at the tunnel wall. After the Helmholtz resonators were arranged according to the 72-cavity optimization scheme, the maximum pressure at the tunnel wall decreased by 10.57% when compared with that before optimization. However, the micro-pressure wave mitigation effect at 20 m from the tunnel exit did not significantly differ from that before the optimization.

... In the last three decades, Japanese and German researchers have studied wave propagation characteristics extensively through field measurements (Matsuo et al. 1996;Mashimo et al. 1997;Fukuda et al. 2006;Adami and Kaltenbach 2008;Heine et al. 2018) and numerical analyses (Miyachi et al. 2016 a, b). The studies have helped tunnel researchers (Mok and Yoo 2001;Howe et al. 2000;Winslow et al. 2005;Iida and Howe 2007;Murray and Howe 2010;Zhang et al. 2017; to develop state-of-the-art entrance hoods that have proven to be the best countermeasure for alleviating MPWs radiating from end of a tunnel. However, to ensure the effectiveness of hoods, especially with overlong tunnels, a thorough assessment of the propagation characteristics must be performed. ...

The parameters of the compression wave propagating in a railway tunnel are significantly influenced by the
large ambient air temperature variation throughout the year. High-speed train entering a railway tunnel produces
a wave of finite amplitude to propagate at sonic speed. The wave attenuates while propagation through viscous
dissipation and inertial forces nonlinearly steepen the wave. As a result of the dependence of sound speed on
air temperature, the wave characteristics are altered with changing temperature. Therefore, it is crucial to
comprehend the impact of ambient air temperature on the properties of the compression wave in order to
construct an aero-acoustically ideal railway tunnel system. The method of characteristics (MOC) has been used
to solve Euler equations with steady and unsteady friction parameters in the current study. According to the
findings, wave attenuation ratio is reducing along the tunnel length, and gradient is rising as train speed
increases. The case study illustrates the key distance within a tunnel where the steepening ratio is at its highest
point. This critical tunnel length is estimated to be 65 times the tunnel hydraulic diameter (300 km/h) for a
particular air temperature (T = 323 K), and it decreases by 15% for a 70 K reduction (323K to 253K) in
temperature. Similarly, the critical length falls by 40% for greater train speeds (500 km/h).

... Based on a railway passenger line project, Liu [9] presented a detailed analysis of the construction difficulties and the buffering effects of a combination of the hat oblique portal and tunnel hood at the entrance under actual working conditions. Zhang et al. [10] presented a 1:20 scale moving model to study the mitigation of micropressure waves by a combination of the hat oblique portal and top opening hood. Guo et al. [11] comprehensively studied the effect of several architectural parameters of the hat oblique portal on micropressure waves in tunnels. ...

... Winslow and Howe (2005) proposed a trumpet-shaped tunnel entrance to alleviate micro-pressure waves. Setting hole and changing the shape of the tunnel hood is also an effective way to reduce the micro-pressure wave (Miyachi and Fukuda, 2021;Zhang et al., 2017Zhang et al., , 2018. A biologically inspired micro-pressure wave buffer cover was installed at the tunnel entrance. ...

Unilateral vertical noise barrier (UVNB), bilateral vertical noise barrier (BVNB) and fully enclosed noise barrier (FENB) are widely used along high-speed railways. The running safety of a high-speed train (HST) faces challenges when entering and exiting a noise barrier in crosswind. A series of computational fluid dynamics numerical simulations of train-noise barrier-crosswind based on the improved delayed detached eddy simulation model and ‘mosaic’ mesh technology are conducted. The influence of different noise barrier types on the aerodynamic load of the carriage is studied. Three buffer structures with different lengths are designed to alleviate the deterioration of aerodynamic performance of HST. Results shows that: The amplitudes of the lift force of the tail car, the lateral force and pitching moment of the head car in the BVNB are the largest, and the amplitude of the yawing moment of the head car in the FENB is the largest. Considering the engineering effects and economic benefits, a buffer structure with a length of six times head car length with a gradual ventilation rate is recommended for project, and the reduction rates of the change rates of the lift and yawing moment are 62.8% and 76.4%, respectively.

... The model test was conducted in the Key Laboratory of Track Traffic Safety of the Central South University in China (Zhang et al., 2017;Wang et al., 2021a). The test bench is divided into upper and lower layers. ...

With the wide use of noise barriers along high-speed railways, the aerodynamic problems of noise barrier caused by high-speed train operation become increasingly prominent. At present, the commonly used noise barrier types of high-speed railway can be classified as fully enclosed and semi-closed (inverted ‘L’ type). The model test of high-speed moving train with scale ratio of 1:16.8 was conducted, and the temporal and spatial laws of aerodynamic pressure of fully enclosed and semi-enclosed noise barriers were compared. These processes were performed to study the difference in the aerodynamic pressure characteristics of noise barriers when high-speed trains at speeds of 350 km/h pass through the two types of noise barriers. On the basis of large eddy simulation turbulence model and ‘mosaic’ grid technology, the corresponding 3D computational fluid dynamics numerical model of train–noise barrier–bridge was established, and the corresponding improvement schemes were proposed to solve the phenomenon of unreasonable pulsation pressure distribution of fully enclosed and semi-enclosed noise barriers. The pressure relief mechanism of the pressure relief hole on the fully enclosed noise barrier and the buffer mechanism of the buffer structure at the end of the semi-enclosed noise barrier are revealed from the perspective of flow field. The main results show that: (1) Compression wave and expansion wave are the key factors affecting the change in the peak pressure inside the fully enclosed noise barrier, while the pressure of the semi-enclosed noise barrier is directly affected by slipstream of the train. (2) The pressure amplitude in the middle of the fully enclosed noise barrier is 2.1–2.7 times of that at the two ends. The amplitude of transverse force at the two ends of semi-enclosed noise barrier is 1.2–1.4 times of that in the middle. (3) In the longitudinal direction of the noise barrier near the train side, the pressure of the measuring point of the semi-enclosed noise barrier decreases with the increase in the measuring point height; The pressure in the middle section of the fully enclosed noise barrier is unaffected by the height of the measuring point. (4) A triangular buffer structure can effectively alleviate the unreasonable vertical pressure distribution phenomenon caused by the train bursting into the semi-closed noise barrier, and the reduction rate of the transverse force amplitude of the end noise barrier is as high as 21.44%. (5) The pressure relief scheme of three holes can effectively alleviate the phenomenon of excessive pressure amplitude in the middle of the fully enclosed noise barrier caused by the passing train, and the reduction rate of pressure amplitude can reach up to 60.5%. The pressure relief holes with an area of 1.7 H × 1.7 H are arranged at 0.25, 0.5, and 0.75 L, where L is the longitudinal length of the noise barrier.

... At present, the reported electrical pressure and temperature integrated sensors are mainly used for normal temperature and low pressure monitoring [3][4][5], and there are few reports on integrated sensors that can be used in high temperature and high pressure harsh environments. Compared with the conventional electrical sensors, optical fiber sensors [6,7] to measure the downhole pressure in oil and gas wells, and the sensitivity of the sensor can reach 230.9 pm/MPa in the range of 0 to 20 MPa. ...

In electrohydrostatic drive actuators, there is a demand for temperature and pressure monitoring in complex environments. Fiber Bragg grating (FBG) has become a promising sensor for measuring temperature and pressure. However, there is a cross-sensitivity between temperature and pressure. A gold-plated FBG is proposed and manufactured, and an FBG is used as a reference grating to form a parallel all-fiber sensing system, which can realize the simultaneous measurement of pressure and temperature. Based on the simulation software, the mechanical distribution of the pressure diaphragm is analyzed, and the fixation scheme of the sensor is determined. Using the demodulator to monitor the changes in the reflectance spectrum in real-time, the pressure and ambient temperature applied to the sensor are measured. The experimental results show that the temperature sensitivity of gold-plated FBG is 3 times that of quartz FBG, which can effectively distinguish the temperature changes. The pressure response sensitivity of gold-plated FBG is 0.3 nm/MPa, which is same as the quartz FBG. Through the sensitivity matrix equation, the temperature and pressure dual-parameter sensing measurement is realized. The accuracy of the temperature and pressure measurement is 97.7% and 99.0%, and the corresponding response rates are 2.7 ms/°C and 2 ms/MPa, respectively. The sensor has a simple structure and high sensitivity, and it is promising to be applied in health monitoring in complex environments with a high temperature and high pressure.

... In a tunnel, the pressure transient induced by the piston effect is strong , and factors such as the tunnel length and buffer structures at the entrance of the tunnel will affect the transient loads in the tunnel Zhang et al., 2017aZhang et al., , 2017bNiu et al., 2020). Using compressible, unsteady, and sliding mesh technologies, Liu et al. (2017b) studied the aerodynamic loads, including the transient pressure, lateral force, and overturning moment, that were caused by a single train moving through a double-track tunnel or two trains passing each other in a tunnel. ...

The pressure integral method is frequently used to obtain the train aerodynamic forces in experiments, but the effect of the pressure pipe length on the pressure amplitude is not understood. In this paper, based on field tests without pressure pipes, the dominant frequency (DF) ranges of the pressure pulsations on the train surface under various conditions, including open-air, crosswind, and tunnel conditions, were analyzed. Then the effect of the pressure pipe length on the pressure amplitude with various pulsation frequencies was investigated. Finally, in a full-scale test under crosswinds, the selected pressure pipe length was applied to verify its reliability and to study the train aerodynamic performance. The results showed that the maximum DF occurred when two trains passed
each other (near 60 Hz), and the DF under crosswinds was the smallest (less than 1 Hz). When the pressure pulsation frequency was less than 1 Hz, the error range of the pressure amplitude was less than 5% with a pressure pipe length of ≤8 m. The pressure pipe is a polyvinyl chloride (PVC) pipe with an outer diameter of 2 mm and an inner diameter of 1.8 mm. The full-scale test results for the windproof ability of different windbreak walls and the aerodynamic forces of the train showed that the current pressure pipe length was reasonable and could reflect the actual operating conditions of the train under crosswinds.

When a high-speed train enters a tunnel, an initial compression wave (ICW) is generated, which radiates out as it propagates lengthways through the tunnel to the exit, forming an uncomfortable micro-pressure wave (MPW). The aim of this research is to develop a scaled device to quickly simulate this aerodynamic phenomenon. Our device achieves this by using the instantaneous release of high-pressure air in the chamber. In the first part of the paper, the reliability of this device is verified by various methods, including an airtightness check, calibration of transducers, and repeatability experiments. Next, the mapping of the parameters of the device to engineering values is discussed. The propagation process of the ICW and the pressure fluctuations in the tunnel are then analyzed, and the discussion centers around a control variable case. Finally, the MPW generated near the tunnel exit is explored and acoustically evaluated. It is found that the initial pressure in the chamber, the opening voltage, and the number of solenoid valves in the experiment can be mapped to the train speed, the characteristic length of train nose, and the blockage ratio, respectively. When the pressure amplitude of the ICW is higher, there will be a certain steepening phenomenon in the propagation process. The pressure fluctuation cycle in the tunnel is calculated as 4× tunnel length/wave velocity, and the amplitude of fluctuation decays exponentially over the cycles. In most cases, the sound pressure level of MPWs near the tunnel exit exceeds the hearing threshold, based on the auditory properties of the human ear.

To effectively control the micro-pressure wave noise radiating from tunnel exits, numerical simulations were conducted to investigate the generation and propagation of such noise at the exits of high-speed metro tunnels. Large-eddy simulation was employed to obtain the near-field unsteady flow field data at the tunnel exit. The Ffowcs Williams–Hawkings (FW–H) acoustic analogy was used to predict the types of sound sources for micro-pressure wave noise. The unsteady flow field data were also utilized for finite element method acoustic analysis to calculate the far-field radiation of micro-pressure wave noise. The accuracy of the numerical methods was verified through moving model tests. The results indicate that dipole noise dominates within the micro-pressure wave noise. The tunnel's inner wall contributes most to the dipole sound sources. Dipole noise radiates outward in the form of semi-ellipsoidal waves, with energy mainly concentrated below 20 Hz and a peak frequency of 4 Hz. Furthermore, the decay of dipole noise in the direction of the tunnel exit follows a similar exponential decay pattern to that of an explosion shock wave. When the train speed exceeds 400 km/h, the human ear can distinctly perceive the sonic booms at the tunnel exit.

Aerodynamic pressure significantly impacts the scientific evaluation of tunnel service performance. The aerodynamic pressure of two trains running in a double-track tunnel is considerably more complicated than that of a single train. We used the numerical method to investigate the difference in aerodynamic pressure between a single train and two trains running in a double-track tunnel. First, the numerical method was verified by comparing the results of numerical simulation and on-site monitoring. Then, the characteristics of aerodynamic pressure were studied. Finally, the influence of various train–tunnel factors on the characteristics of aerodynamic pressure was investigated. The results show that the aerodynamic pressure variation can be divided into stage I: irregular pressure fluctuations before the train tail leaves the tunnel exit, and stage II: periodic pressure declines after the train tail leaves the tunnel exit. In addition, the aerodynamic pressure simultaneously jumps positively or drops negatively for a single train or two trains running in double-track tunnel scenarios. The pressure amplitude in the two-train case is higher than that for a single train. The maximum positive peak pressure difference (PSTP) and maximum negative peak pressure difference (PSTN) increase as train speed rises to the power from 2.256 to 2.930 in stage I. The PSTP and PSTN first increase and then decrease with the increase of tunnel length in stage I. The PSTP and PSTN increase as the blockage ratio rises to the power from 2.032 to 2.798 in stages I and II.

A high-speed train with wings (HSTW) is a new type of train that enhances aerodynamic lift by adding wings, effectively reducing gravity, to reduce the wear and tear of wheels and rails. This study, based on the RNG k−ε turbulence model and employing a sliding grid method, investigates the aerodynamic effects of HSTWs with different angles of attack when passing through tunnels. The precision of numerical simulation method is validated by data obtained through a moving model test. The results show that the lift of the HSTW increases upon entering the tunnel, with an average lift in the tunnel of 33.3% greater than that in the open air. The angle of attack is reduced from 12.5° to 7.5° when the train enters the tunnel, which can better reduce the lift fluctuations and concurrently also reduce the peak-to-peak pressure on the surface of the train and the tunnel, which is conducive to the train passing through the tunnel smoothly; hence, the angle of attack for the HSTW when passing through a tunnel is adjusted 7.5°. Furthermore, a comparison between the high-speed trains with and without wings demonstrates that the frontal pressure of the trains increases due to the blockage effect caused by the wings, while the rear of the trains experiences decreased pressure, which is primarily influenced by the wing wake. The outcomes of this study provide technical support for HSTWs passing smoothly through tunnels.

Falling debris in high-speed railway tunnels is a prevalent and serious safety concern. Debris falling from tunnel vaults may impact the train surfaces, pantographs and window glasses, resulting in economic losses and even injuries to individuals. The complex train winds inside a railway tunnel are a nonnegligible factor influence the flight trajectory and impact position of falling debris. Therefore, understanding the flight behaviors of falling debris considering the train wind effects is crucial for engineering managers to make informed decisions that improve the operational safety of high-speed trains in tunnels. In this study, we develop a device that controls the automatic drop of a tunnel debris in a high-speed train ejection experiment. By employing the experiment and moving-overset-mesh method, the flight behavior of falling debris from the vault of a railway tunnel under the influence of train winds, including the translation behavior, rotation behavior, aerodynamic coefficient, and corresponding flow mechanism, are investigated. The reliability of the high-speed train ejection experiment is confirmed through repetitive tests. The moving-overset-mesh simulation is verified by a grid independence test and comparisons with the experimental results. The research findings unveil a distinctive two-stage flight behavior of falling debris influenced by the wind generated from the passing train. Specifically, the first stage of debris flight is primarily governed by the wind profile near the train body, while the second stage is characterized by the tail airflow. Moreover, there exists a difference in the flight behavior between square and circular plate debris, which can be attributed to the variation in distribution and scale of vortex structures that form and adhere to the falling debris.

The micro-pressure wave (MPW) is a major source of noise pollution around the railway tunnel environment and adversely affects the local building structure and the daily lives of residents. The main approach for alleviating MPWs is to install the tunnel hood at the mouth, and the specification design of the tunnel hood is of great significance to effectively mitigate the MPW. However, the traditional CFD and model-based experimental methods usually utilized for tunnel hood design are time-consuming and inefficient. Therefore, this paper presented a rapid design method that combined the CFD method and proper orthogonal decomposition (POD) to design the parameters of the tunnel hood more efficiently. The initial transient database was first obtained from the numerical calculation verified by the model experiment, and then the database was extracted characteristically and reconstructed considerably using the POD method. The feasibility and accuracy of the proposed method were validated by implementing the demonstration case of a typical tunnel hood design. It can be seen from the research results that the determination coefficients (R2) of all test cases for transient results between the CFD method and the proposed method are over 0.99; the optimal parameter of this tunnel hood obtained from the POD reconstruction can achieve an approximately 60% mitigation rate of the MPWmax, which is further verified by the numerical result with a discrepancy of merely 1.87%. Compared with the traditional CFD method, the proposed method can reduce nearly 98% of the total design time with a favourable prediction precision.

As the subway lines are rapidly developing in the cities, the pressure wave in different subway tunnel constructures is urgently needed to be studied and receded. In this study, a subway tunnel pressure wave experimental system was designed, constructed, and tested. The influence of train model head shape, train model speed, shaft number in the tunnel, and bypass number in the tunnel on the pressure wave amplitude were experimented with and analyzed. The results show that the train model head shapes significantly impact the amplitude of the initial compression wave in the tunnel. The blunter train model head generates a greater amplitude of the initial compression wave. When the train passes through a single-track tunnel, the maximum positive pressure amplitude of the pressure wave in the tunnel is at the first compression wave at the tunnel entrance. The maximum negative pressure value in the tunnel is at the superposition of the initial compression wave reflected from the first time and the train’s body, which is related to the length of the train’s body, tunnel length, train’s speed, and sound speed. The shaft set in the tunnel decreases the amplitude of the initial compression wave in the tunnel space behind, but it will increase the pressure wave’s amplitude reflected in the tunnel when the train passes through the shaft. After the bypass tunnel is added, the initial compression wave propagation in the tunnel behind the bypass tunnel is receded. It also increases the negative pressure amplitude when the train passes.

When a train passes through underground stations quickly, strong transient pressure fluctuations will generated. In this paper, a moving model experimental device is adopted to explore the distribution of transient pressure on the surfaces of train and platform screen doors when the train passes through an underground station. An analysis of the effect of ventilation shaft locations on alleviating transient pressure was also carried out. The findings indicate that the pressure fluctuations of corresponding monitoring points on different platform screen doors are quite different. The ventilation shaft can affect the pressure peak values, and the influence characteristics of the shaft at different locations are quite different. The shaft located next to the platform has the most profound impact on alleviating the transient pressure amplitude on the surfaces of the train and platform screen doors. In comparison to a station without a shaft, the pressure amplitude of the monitoring point H2 arranged on the train surface can be reduced by 47.1%, and the pressure amplitude of the monitoring point P1 on the surface of platform screen doors decreases by 71.3% when the shaft was set near the platform.

Noise barriers need to be installed along high-speed railway lines to protect nearby inhabitants from the noise pollution caused by the running of high-speed trains (HSTs). The vertical noise barrier is the main structural type. However, when an HST passes through the noise barriers sited along the track, significant and transient aerodynamic pressure will act on the surface of the noise barriers, resulting in strong dynamic responses and even fatigue damage. Therefore, it is important to determine the train-induced aerodynamic load on the barrier surface and analyze the dynamic behaviors of the noise barriers under such a load for its structural design and to guarantee its safety and durability. This paper is a systematic review of the current literature on the aerodynamic load and dynamic behavior of vertical noise barriers; it includes (1) a summary and analysis of characteristics of such aerodynamic pressure and relevant influencing factors, (2) an introduction to measurement methods of aerodynamic load and relevant pressure models on the surface of noise barriers, and (3) a description of the dynamic response and fatigue analysis of noise barriers under such loads. Finally, potential further studies on this topic are discussed, and conclusions are drawn.

The nonlinear aerodynamic loads and dynamic responses caused by the crosswind when two trains pass each other are extremely complex, and guaranteeing safety under these circumstances is difficult. To compare the difference in nonlinear loads and dynamic response between one train and two trains passing each other under crosswinds, the Renormalization Group k- turbulence model and the “mosaic” grid technology are used to establish a variety of 3D numerical models of train–tunnel–embankment. The variation law of aerodynamic load in the numerical model is highly consistent with the test data, and the maximum error is less than 7%. First, the aerodynamic performance differences are compared with the aspects of nonlinear load amplitude and power spectral density, and the difference mechanism is disclosed by the flow field. Then, based on a segmental loading method, a coupled dynamic response analysis model (wind–train–tunnel–embankment) is used to analyze the difference rule of the derailment coefficient and the rate of wheel load reduction (RWLR). The key conclusions are as follows: The pulse impact produced by trains meeting aggravates the aerodynamic load amplitude. The amplitude of rolling and yawing moments on the head train increases by 78.31% and 30.88%, respectively. When the crosswind speed exceeds 20 m/s, the RWLR enters the dangerous zone.

Vortex shedding at the tail of a high-speed train changes the aerodynamic characteristics of the train, which affects the safety and stability of train operation. This paper takes CR400AF as the research object, and uses dynamic monitoring points to realize the whole process monitoring of the flow field at the tail of the train running in open air and in tunnel for the first time. The wake of the train in different infrastructure scenarios is analyzed by the proper orthogonal decomposition method. The study found that the wake vortex structure is quite different when the train runs in different scenarios, and the turbulent kinetic energy intensity of the wake in tunnel is higher than that of the open air running. Modal decomposition method can identify flow structures that have a large impact on train aerodynamics. Through frequency analysis, it is found that the modal frequency obtained from the decomposition is higher when running in open air than when running in tunnel. With the increase of train speed, the modal strouhal number increases when the train is running in open air, and decreases when the train runs in tunnel. After the train enters the tunnel, the reverse movement of the air around the train body suppresses the development and separation of the boundary layer, which is the main reason for the low frequency of wake vortex shedding in tunnel. The stability of the train running in tunnel is worse than that when running in open air, which is closely related to the more complex flow structure around the car body and the drastic change of aerodynamic force when running in the tunnel.

Tunnel passing at high speed produces aerodynamic load on railway trains, which may bring about fatigue failure on the car body, and damages passenger comfort due to interior penetration of the alternating wave. In this work, the air suction experiment approaches were developed. It performs excellently through internal and external loading utilizing valve controlling strategies. It is validated with an in-transit vehicle test when the train runs through 3 different tunnel lengths. The relative deviation between simulation and vehicle tests goes no more than 5.0%. Research outcome indicates that the proposed method provides an important experiment means for passenger comfort and car-body fatigue behavior research.

The complex wind effects around platform screen doors (PSDs) caused by train-induced piston wind effect and positive micropressure waves in subway station platforms are investigated. Numerical modeling of the wind field around full-scale PSDs with real gaps under different inflow conditions is developed to analyze the pressure distributions on and around the PSDs and the corresponding recirculation regions in the frontal and rear PSD areas with computational fluid dynamics (CFD) method. An equivalent porous media model is developed to obtain the relationship between the pressure difference and wind velocity based on Darcy–Forchheimer’s Law. It includes a viscosity loss term and an inertial loss term in the simulation of the air leakage flow generated from the PSD gap. The coefficients of these two terms are estimated from the CFD results from the full-scale models. The complicated flow field originated from the gaps is the main cause of the large wind pressure on the PSD, and the flow velocity on the platform may significantly affect the comfort of pedestrians and of the safety design of the PSD system.

The present study numerically explored the aerodynamic performance of a novel railway tunnel with a partially reduced cross-section. The impact of the reduction rate of the tunnel cross-section on wave transmissions was analyzed based on the three-dimensional, unsteady, compressible, and RNG k−ε turbulence model. The results highlight that the reduction rate (S) most affects pressure configurations at the middle tunnel segment, followed by the enlarged segments near access, and finally the exit. The strength of the newly generated compression wave at the tunnel junction where the cross-section abruptly changes increases exponentially with the decrease of the cross-sectional area. The maximum peak-to-peak pressure ΔP on the tunnel and train surface for non-uniform tunnels is reduced by 10.7% and 13.8%, respectively, compared with those of equivalent uniform tunnels. Overall, the economic analysis suggests that the aerodynamic performance of the developed tunnel prototype surpasses those conventional tunnels based on the same excavated volume.

A systematic field test was conducted for aerodynamic pressure near the entrance of the double-track fully enclosed sound barriers (FESBs). The generating mechanism of pressure was revealed by referring to the slipstream distribution around the moving train and considering the influence of marshalling length, speed and streamline of trains. Results show that near the entrance, the compression wave caused by the head car is predominant and determined by the maximum, minimum and peak-to-peak pressure, while near the exit, the negative and positive peak pressure are, respectively, triggered by the head car and tail car. Uneven pressure distribution along the circumference of the FESB wall and the greater pressure is on the wall near the running train. The head car of double-connection electric multiple units (EMUs) generates greater pressure near the entrance than that of common EMUs, and the tail car of double-connection EMUs causes weaker pressure transient, while near the exit, the head car of double-connection EMU induces weaker pressure. Even if the train speed increases in a small range, the pressure near the entrance/exit of the FESB increases, and the blunter the train is, the greater and the more evenly distributed pressure on the FESB will be.

Subway is an increasingly important means of transportation, the influence of the piston effect on the train has attracted extensive attention of researchers. Nowadays, the train speed is increasingly faster, the piston effect caused by the high-speed train is increased accordingly and the pressure fluctuation in tunnel is more complex. In this study, the numerical simulation method is used to study the pressure fluctuation inside and outside the train when the train passes through the tunnel and station. The influence of train speed, mode of the train passing through the station and number of airshafts on the train pressure is analyzed. It is found that both the external and internal pressures of the train increase significantly with the increases of the train speed, and the head carriage bears the most pressure. As the mode of the train passes the station changed, there is a slight variation of train pressure. The airshafts can relieve the pressure inside the train. Finally, passenger comfort under different operating conditions is studied. Different air tightness indexes of the train are compared and analyzed. This study will contribute to the improvement of subway comfort and provide references for the design and operation of the train.

Inspired by shark’s skin in nature, a non-smooth surface could be an ideal model for changing the flow characteristics of fluids on the object surface. To analyze the effect of a non-smooth surface with concaves on the maglev train aerodynamic performances and to investigate how the concave size affects the aerodynamic forces and flow structure of a maglev train, four 1/10th scaled maglev train models are simulated using an Improved Delayed Detached Eddy Simulation (IDDES) method. The numerical strategy used in this study is verified by comparison with the wind tunnel test results, and the comparison shows that the difference was in a reasonable range. The results demonstrate that the concaves could effectively reduce the tail car pressure drag, thus reducing the total drag, and that the smaller the concave size was, the better the drag reduction effect would be. The change in the lift with the concave size was more significant than that of the drag, and the tail car lift of R1 (0.0012H), R2 (0.0024H), and R3 (0.0036H) train models was 30.1%, 43.0%, and 44.5% less than that of the prototype, respectively. In addition, different flow topologies of the wake are analyzed. The width and height of the vortex core of the counter-rotating vortices tended to decrease with the concave size. Thus, from the point of view of ensuring the operating safety of a maglev train, a non-smooth surface with small-size concaves is recommended.

When a compression wave generated by a high-speed train entering a tunnel propagates through the tunnel and arrives at the tunnel exit, an impulsive pressure wave (micro-pressure wave) is radiated from the tunnel exit. Improving the train nose shape is one of the techniques for suppressing the micro-pressure wave. Furthermore, tunnel entrance hoods are required for long concrete slab tunnels in order to suppress the micro-pressure wave. The effect of the tunnel entrance hood on the compression wave generated by the train can be evaluated by means of a rapid computational scheme devised and validated experimentally by Howe et al. In this study, the optimal longitudinal distribution of the cross-sectional area of the train nose shape was determined by using the rapid computational scheme and a genetic algorithm. The effect of the nose shape optimization was confirmed through experiments using scale models.

This study concerns the reduction of the pressure gradient of the compression wave generated in a tunnel by the entry of a high-speed train. Influences of different parameters such as the train/tunnel blockage ratio, the shape of the train nose, the geometry of the entrance hood, are investigated by means of reduced-scale experimental simulations. An improved relation between the pressure coefficient and the pressure gradient coefficient which takes into account the aspect ratio of the train nose is proposed. Finally, a procedure to optimise a constant sectional area entrance hood is described in detail

In order to accelerate a heavy train model with great dimensions to a speed higher than 300 km h−1 in a moving train model testing system, compressed air is utilized to drive the train model indirectly. The gas from an air gun pushes the piston in an accelerating tube forward. The piston is connected to the trailer through a rope, and the trailer pulls the train model to the desired speed. After the testing section, the train model enters the deceleration section. The speed of the train model gradually decreases because of the braking force of the magnetic braking device on the bottom of the train model and the steel plates fixed on the floor of this device. The dissipation of kinetic energy of the trailer is also based on a similar principle. The feasibility of these methods has been examined in a 180 m-long moving train model testing system. The speed of the trailer alone reaches up to 490 km h−1. Consequently, a 34.8 kg model accelerates up to 350 km h−1; the smooth and safe stopping of the model is also possible.

This paper reports the numerical research of tunnel hood effects on high speed train-tunnel compression wave. The three-dimensional simulation with real geometry is carried out by the implementation of a commercial computational code. The train speed is 350 km/h. The train/tunnel blockage ratio is 0.115. Nine different types of tunnel hoods were studied. The calculation results showed that the hood length, the hood cross sectional area and the ventilation holes might have significant influence on the first compression wave, and inclined entry or asymmetric distribution of the ventilation holes is not available for alleviating the impulsive wave.

An optimally designed entrance portal must be capable of minimizing the maximum growth rate of the compression wave generated when a high-speed train enters a tunnel. A theoretical and experimental investigation has been made to determine the changes in compression wave characteristics produced when the portal is 'scarfed' with tapering side walls. It is concluded that portal modifications of this type are unlikely to produce a significant reduction in the maximum compression wave growth rate. Small decreases in growth rate are possible (up to about 15%) for scarf walls extending a distance beyond the tunnel entrance of the order of the tunnel height, but little or no additional improvement is achieved with longer walls.

The work presented in this paper concerns the first compression wave generated in a tunnel when a high-speed train enters it. This wave is the first of successive compression and expansion waves which propagate back and forth in the tunnel. Once generated at the tunnel entrance, its amplitude and gradient vary according to the train and tunnel characteristics. These waves provoke: (a) an aural discomfort for train passengers, (b) mechanical stresses on train and tunnel structures, and (c) emission of impulsive noises outside the tunnel. A reduced-scale test method, using low-sound-speed gas mixtures, has been developed and validated by using newly available European full-scale test-results. It can reproduce quite well the three-dimensional effects due to the train geometry and its position in the tunnel. The study also clearly points out that three-dimensional effects on the front of the first compression wave are attenuated with distance from the tunnel entrance and that the wave front can be considered well established and planar for distances larger than four times the tunnel diameter. Characteristics of the planar wave are in good agreement with Japanese results. The reduced-scale train Mach number has been extended up to 0.34 to determine its test domain. Our study clearly shows that, as far as the characteristics of the wave front of well-established planar first compression wave are concerned, axially symmetrical models can advantageously replace three-dimensional models, provided that the longitudinal cross-sectional area profile is the same for both configurations. This feature yields the following train nose design procedure: first determine the cross-sectional profile of a train nose against train–tunnel interactions by means of axially symmetrical configuration, then give a three-dimensional shape for drag and stability optimisation.

The influence of the Reynolds number on the aerodynamic force and pressure of a train was investigated experimentally at yaw angles of 0° and 15°. Two kinds trains were scaled at 1:8 and 1:20, respectively, and the Reynolds number, based on the train height, ranged from 3.02×10⁵ to 2.27×10⁶. The pressure distribution along a train at yaw angles of 0° and 15° was researched, and the results are compared herein. The difference in Reynolds number effect between the head and tail cars is also discussed. The results show that the lift coefficient of a train increases with an increase in Reynolds number at a yaw angle of 15°, and the other force coefficients decrease with an increase in Reynolds number. There are significant differences between the positive and negative pressures in terms of the Reynolds number effect. The yaw angle weakens the Reynolds number effect on the pressure coefficient on the head car, whereas the influence of the yaw angle on the Reynolds number effect on the pressure coefficient for the tail car is relatively complex.

A computer programme is used to predict the pressure histories on the walls of a tunnel when a train enters and passes through the tunnel at speed. The programme is capable of simulating the velocity and pressure histories in complex tunnel systems during the passage of any number of trains. Comparisons are made with pressure histories recorded by transducers mounted on the wall of the laboratory model described in the first of these two papers. By carefully choosing empirical coefficients in order to give a good ft to the data, excellent correlation is obtained for the basic case of a train in a simple tunnel. The principal features of the pressure histories in a wide range of tunnel configurations are also well simulated using the same empirical data. Comparisons are also made with full scale measurements obtained in Patchway Tunnel. The correlation is not as good as with the laboratory measurements. However, it is sufficiently close for the accompanying predictions of the influence of various modifications to the tunnel to be regarded as valid. It is shown that there are significant benefits to be gained from entrance modifications, but that these cannot alone provide a complete solution. Pressure fluctuations generated during train exit must also be taken into account. (A)

According to the 100m
2 double-line tunnel cross-section which is generally used in high-speed railway of China, this paper develops a tunnel - air - train simulation model, based on the three-dimensional incompressible Navier - Stokes equations and the standard k − ε turbulence model. This model can simulate two situations one is that a single train runs through a tunnel normally while the other is that another train runs beside a train parked in the tunnel. Time-history variation rules and space distribution characteristics of train wind are studied respectively at 120 km, 200 km, 250 km, 300 km and 350 km per hour. Furthermore, the authors discuss train wind influence on personnel safety on evacuation passageways. In addition, the authors give out analytically the results of the numerical simulation. The results show that: Train wind is complex three-dimensional flow changing with time and space, so people should avoid activities at dangerous time and places; since personnel safety may be threatened by train wind in the two situations above, therefore, effective measures should be taken to avoid accidents.

Based on analyzing the generating mechanism of micro-pressure wave at high-speed railway tunnel exit, with one-dimensional unsteady-compressible- nonisentropic air flow theory and round-piston radiation theory with infinite baffle plate, the rules of micro-pressure waves generated by high-speed train near tunnel exit under different shape hoods were studied, the influences of various shapes and parameters of hoods on the waves were qualitatively and quantitatively analyzed. It is indicated that the wave intensity evidently decrease with the length and cross-section area increasing of line-type, parabola-shaped and discontinuous-type hoods, the effect of discontinuous-type hood is evidentest; when hood cross-section area is constant, but hood construction is perforated, the choice for the best structural parameters needs an integrated plan contrast although the wave intensity can be greatly reduced.

After having evaluated a 3-dimensional Eulerian code’s capability to predict the wavefront’s pressure gradient of the primary pressure waves generated by trains entering a tunnel, SNCF’s Research and Technology Department was assigned to test the tool via a study bearing upon tunnel portal extensions which attenuate the pressure gradient of the entry wavefront. As a first step, taking into account the numerical and computational constraints, the model was sized to permit reasonably quick simulations of many train-tunnel entry cases. As a second step, the parametric study was made on the particular case of the Terranuova le Ville tunnel and served to assess the influence of various geometrical parameters relating to short, flared or perforated tunnel portal extensions.

Entering a tunnel a high-speed train generates
a pressure wave, which propagates along the tunnel and is partly reflected at the opposite tunnel portal. This wave leads to some severe problems like loads on the installations inside of the tunnel, discomfort of the passengers or even micro-pressure waves at the end of the tunnel. The tunnel-simulation facility Göttingen (TSG) was built in order to analyse these pressure changes and to develop systems, which smooth the pressure increase and reduce the pressure-depending problems in train-tunnel entry. The TSG is a moving-model rig, which allows a very realistic investigation of train-tunnel interaction. The train used is an ICE3-model made of carbon fiber scaled 1:25. The train speed ranged from 30 up to 45 m/s. The results of the experiments done in the TSG show, that the pressure gradient can be reduced by about 45 % using an extended, vented tunnel portal.

A high-speed train entering a tunnel generates a strong pressure jump which propagates inside the tunnel. This paper presents investigations on the formation of the compression wave generated by the entering of the train nose: experimentally, with a scale-model facility, tests have been undertaken from 0 to 30 m/s with different lengths of train nose and different shapes of entry portals; numerically, a one-dimensional unsteady compressible flow calculation method based on the method of characteristics has been developed and compared to experimental results.

The current work experimentally investigates the pressure transients induced by a high-speed train passing through a station as well as two trains passing by each other at stations. The experiments were performed by using 1/20th scale train models with a head car and an end car on a moving model rig at different speeds. Pressure transients were measured using pressure sensors on platform screen doors and car body surfaces. The characteristics of pressure transients on the car body surface and platform screen doors when a single train passes through stations and two trains pass by each other at stations are discussed. The influence of the laws of train speed, crossing position and other parameters on the pressure change of the platform screen doors and on board is analysed.

AEA Technology Rail have undertaken 1/25 model-scale tests for the TRANSAERO Project using their unique Moving Model Rig. This catapults model trains along a 146 m test track at full-scale train speeds, allowing measurements to be made of the aerodynamic effects generated. Pressures were measured for a shortened model ETR500 train for direct comparison with data gathered during full-scale tests undertaken in Italy. The model was also used to validate numerical simulation predictions carried out for the TRANSAERO Project. Additional model-scale tests were made featuring train nose and track spacing configurations not tested at full-scale. The results have increased the understanding of the importance of these features adding to the knowledge compiled to assist the design of European high speed trains of the future.

The slipstream of high-speed trains is investigated in a wind tunnel through velocity flow mapping in the wake and streamwise measurements with dynamic pressure probes. The flow mapping is used to explain the familiar slipstream characteristics of high-speed trains, specifically the largest slipstream velocities in the near wake. Further, the transient nature of the wake is explored through frequency and probability distribution analysis. The development of a wind tunnel methodology for slipstream assessment is presented and applied, comparing the output to full-scale results available in the literature. The influence of the modelling ballast and rail or a flat ground configuration on the wake structure and corresponding slipstream results are also presented.

A three-dimensional flow induced by a practical high-speed train moving into a tunnel is studied by the computation of the compressible Navier-Stokes equations with the zonal method. The transient flow field induced by tunnel entry is investigated with the focus on the compression wave which is the source of the booming noise at the tunnel exit. The results reveal a pressure increase inside the tunnel before tunnel entry, the one-dimensionality of the compression wave, the histories of the aerodynamic forces, etc. The computed pressure histories inside the tunnel agree with the field measurement data. The flow fields are also computed for cases where the train runs on differently positioned tracks into the tunnel. The results indicate that the wavefront of the compression wave is affected by the train position and this phenomenon is explained by the parameter υwatt.

This paper relates to the parametric study of tunnel hoods in order to reduce the shape, i.e. the temporal gradient, of the pressure wave generated by the entry of a High speed train in tunnel. This is achieved by using an in-house three-dimensional numerical solver which solves the Eulerian equations on a Cartesian and unstructured mesh. The efficiency of the numerical methodology is demonstrated through comparisons with both experimental data and empirical formula. For the tunnel hood design, three parameters, that can influence the wave shape, are considered: the shape, the section and the length of the hood. The numerical results show, (i) that a constant section hood is the most efficient shape when compared to progressive (elliptic or conical) section hoods, (ii) an optimal ratio between hood's section and tunnel section where the temporal gradient of the pressure wave can be reduced by half, (iii) a significant efficiency of the hood's length in the range of 2-8 times the length of the train nose. Finally the influence of the train's speed is investigated and results point out that the optimum section is slightly modified by the train's speed.

In confined spaces the air movements around high speed trains may be amplified. Moving-model aerodynamic experiments were undertaken to identify the fundamental changes to train-induced air movements by firing a 1/25th scale high-speed train past instrumented walls and through box-shaped tunnels. The effect of confinement on velocities in the boundary layer and wake are assessed. Moreover the peak gusts are analysed using a prescribed European methodology to determine whether confined spaces cause the flow to exceed acceptable criteria. All results showed significant increases in velocity in the near wake, with the gusts exceeding allowable limits of velocity at positions extending far from the train side. The pressure transient increased in magnitude with increasing confinement, although the increases were lower than those predicted by European standards.

The theory and practice of train-induced aerodynamic pressure loads on surfaces near to the tracks is compromised by an incomplete understanding of trains operating in short tunnels, partially enclosed spaces, and next to simple structures such as vertical walls. Unique pressure-loading patterns occur in each case. This work has been carried out to obtain a fundamental understanding of how these loading patterns transition from one to the other as the infrastructure becomes more confined. It also considers the impact of the results on two separate European codes of practice applying to tunnels and other structures. A parametric moving-model study was undertaken, transitioning from the open air to single and double vertical walls, partially enclosed spaces, short single-track tunnels and a longer tunnel. The train model was based on a German ICE2, and was fired at 32 m/s past the structures. Multiple surface pressure tappings and in-flow probes were used, providing the opportunity to assess the three-dimensional nature of the pressure and velocity fields. The experiments successfully mapped the transition between the three loading patterns and isolated the geometric changes. Further loading patterns were discovered relating to the length of the train, the length of the tunnel and the distance from the tunnel entrance. The three-dimensional nature of the pressure was related to the length of the tunnel and the distance from the tunnel entrance. Issues surrounding the lack of provision in codes of practice for short tunnels were discussed.

An obvious pressure change and a micro-pressure wave are generated when a train enters a tunnel at high-speed, which impacts on the comfort of passengers and the environment around the tunnel. Thus, it is necessary to study the aerodynamics of tunnels in order to reduce the pressure change and micro-pressure wave. Our laboratory owns an advanced moving-model device that can simulate two trains crossing in the open air or trains entering a tunnel, with a maximum speed of 400km/h. This paper studies the pressure change, the micro-pressure wave and a series of hoods using three-dimensional numerical simulations and moving-model experiments. From a comparative study, we obtain rules governing the influence of hoods on the micro-pressure wave, and reasonable shapes and parameters of hoods are designed.

The unsteady aerodynamic effects in railway tunnels are generally analyzed by quasi one-dimensional numerical simulations which can give the effects of the pressure waves encountered in the tunnels with a low CPU cost. In the present work, a new method for predicting the evolution of the pressure in the tunnel is presented. This method, based on the signature of the pressure waves during their propagation, requires lower computational efforts, gives results with a precision equivalent to those obtained by conventional methods, and permits to investigate more complex situations of train circulation in simple tunnel. The simulation of the tunnel length influence on the pressure changes permits to define a very short, a short and a long tunnel. The crossing of two High speed trains in tunnel is simulated with different delays in the time entry of the trains, and it is shown that the maximum pressure change in the tunnel or on the trains is function of this time shift.

This paper reports numerical computations of the train–tunnel interaction at a tunnel entrance with real dimensions. Simulations were carried out by the FEM using the three-dimensional compressible Euler equation. The train speed was 300km/h. For a single-track tunnel, four kinds of tunnel entrance shapes were studied to investigate the formation of the compression wave front at the tunnel entrance. This study shows the possibility of a partial change in the compression wave front by means of the optimal combination of the degree of the tunnel entrance slopes and holes in the tunnel entrance ceiling. The results can be used for countermeasures against the boom noise at the tunnel exit, for the air tightness design of the train body shell and fatigue damage of the tunnel wall and structure. The compression wave fronts at the tunnel entrance directly affected the pressure drop in the tunnel and the booming noise intensity at the tunnel exit.

A compression wave is generated when a high-speed train enters a tunnel. The wave propagates ahead of the train at the speed of sound. In a long tunnel nonlinear steepening of the wavefront produces the emission of a strong micro-pressure wave (mpw) from the distant tunnel exit. The mpw can produce structural damage to the tunnel and rattles in surrounding buildings. Nonlinear steepening can be countered by increasing the initial rise time of the compression wave by installing a tunnel entrance ‘hood’ consisting of a nominally uniform extension of the tunnel of larger cross-section. In this paper a theoretical examination is made of the influence on the wave of the rapid change in tunnel cross-section in the transition region between the tunnel and hood. It is shown that by optimally profiling the cross-sectional area changes across this region it is possible to minimize the amplitudes of second and third peaks of the compression wave pressure gradient. By this means the amplitudes of the secondary peaks in the micro-pressure wave are greatly reduced.

A practical analytical scheme is proposed for making rapid numerical predictions of the compression wave generated when a high-speed train enters a tunnel fitted with a vented entrance hood. The method synthesises results from several analytical procedures developed during the past few years for treating different aspects of the tunnel-entry problem, including the effects of change in cross-sectional area at the hood-tunnel junction, high-speed jet flows from windows distributed along the length of the hood, frictional losses associated with separated turbulent flow between the tunnel and hood walls and the train, and the influence of train nose shape. Details are given in this paper for the simplest case of circular cylindrical tunnels and hoods of the type used in model scale testing and design studies. Typical predictions can be made in a few seconds on a personal computer (in contrast to the tens or hundreds of hours required for simulations using the Euler or Navier–Stokes equations on a high performance supercomputer). A summary is given of selected predictions and their comparisons with experiments performed at the Railway Technical Research Institute in Tokyo at train Mach numbers as large as 0.35(∼425km/h).

An analysis is made of the compression wave generated when a high speed train enters a tunnel. Operations in the near future are expected to be at Mach numbers M ranging in value up to 0.4. Non-linear steepening of the wave in a very long tunnel exacerbates the environmental damage caused by the subsequent radiation of an inpulsive micro-pressure wave from the far end of the tunnel. The compression wave profile depends on train speed and the area ratio of the train and tunnel, and for M < 0.2 can be estimated to a good approximation by regarding the local flow near the tunnel mouth during train entry as incompressible. The influence of higher train Mach numbers is investigated for the special case in which the tunnel is modelled by a thin-walled circular cylinder, of the type frequently used in model scale tests. This is done by representing the nose of the train by a distribution of monopole sources, and calculating their interaction with the mouth of the tunnel by using the exact acoustic Green's function for a semi-infinite, circular cylindrical tunnel. Empirical formulae valid up to M = 0.6 are obtained for the compression wave amplitude and for the maximum initial pressure gradient (which determines the amplitude of the micro-pressure wave). Predictions of the theory are found to be within 5% of measurements made in recent experiments. (C) 1998 Academic Press Limited.

Following the Series 300, which was introduced in March 1993, the next-generation Series 700 train-set was put into commercial operation on the Tokaido-Sanyo Shinkansen lines in March 1999. The Series 700 has a number of aerodynamic improvements, focusing on the nose shape, the area around the carbody, car coupling areas, the pantograph and the pantograph cover. These improvements have resulted in lower wayside noise and pressure fluctuations, improved riding comfort in tunnels, reduced power consumption and increased speed (285 km/h) over some track sections. This paper reports the development of the Series 700 train-set by describing the techniques used to improve the aerodynamic characteristics of the car and the results of the improvements in comparison with the Series 300 train-set.

An analysis is made of the compression wave generated when a high-speed train enters a tunnel with a flared portal. Nonlinear steepening of the wavefront in a very long tunnel is responsible for an intense, environmentally harmful, micro-pressure wave , which propagates as a pulse from the distant tunnel exit when the compression wave arrives, with amplitude proportional to the maximum gradient in the compression wavefront. The compression wave profile can be determined analytically for train Mach numbers M satisfying M2⪡1, by regarding the local flow near the tunnel mouth during train entry as incompressible . In this paper, the influence of tunnel portal flaring on the initial thickness of the compression wave is examined first in this limit. The shape of the flared portal is “optimal” when the pressure gradient across the front is constant and an overall minimum, so that the pressure in the wavefront increases linearly . This linear behaviour is shown to occur for a flared portal extending a distance ℓ into the tunnel from the entrance plane (x=0) only when the tunnel cross-sectional area S (x) satisfiesS (x)A=1[A/AE−(x/ℓ)(1−A/AE)], −ℓ

An experimental facility was developed for investigating pressure waves generated by high-speed trains. The facility launches a 1/30 scale model conforming to the actual shape of the train and enables measurements to be carried out with the same geometric configurations at full scale. The train models are launched using compressed air. A mathematical model is developed to predict the performance of the experimental facility. This model allows the optimum values of the design parameters of the facility to be determined in order to achieve a given target velocity and to control the launching velocity by adjusting the pressure of the compressed air. Measurement of the flow in the experimental facility shows that the facility performs as designed by the mathematical model and is capable of launching a train model at velocities greater than 500km/h. Pressure waves generated by a train moving into a tunnel are measured, and the experimental data agree well with field measurements. The effect of the train nose on the strength and form of the pressure waves is also discussed.