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Oblique tunnel portal effects on train and tunnel aerodynamics based on moving model tests
Abstract
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.
... 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.
... Therefore, the development of test devices for the simulation of the various movements of the vehicles in an atmospheric environment and the measurement of the aerodynamic parameters has great significance to the scientific progress and the engineering design of high-speed trains and aviation. 1,2,8 Although some advantages of moving model test (MMT) over wind tunnel test in the simulation of the movement patterns are gradually emerging, 3,[9][10][11][12][13][14][15][16] the complete principle and technology of a moving model rig (MMR) with high speed, strong driving power, and corresponding methodologies for aerodynamic drag assessment are still lacking in the literature. ...
... In the investigation of the aerodynamic characteristics of high-speed trains and fixed-wing aircraft, the tests are typically performed with relative motion between the model and the air. 1,[9][10][11][15][16][17][18] To apply the model data to an actual vehicle, it is usually required to correct the errors in the measured data caused by the differences of the Reynolds number (Re). 8,17,18 If the model data will be directly extrapolated to the full scale, not only must the shapes of the model and full-scale vehicles be as similar as possible but the corresponding Re values must be nearly equal, or the Re of the model must be in the supercritical region (i.e., the self-simulation region). ...
... For aerodynamic tests of high-speed trains, MMRs that are capable of driving models with large masses to actual train operating speeds have been developed in the UK, Germany, and China. 3,9,10 Other countries, including Japan, South Korea, and France, have carried out corresponding tests using simple moving model devices and smaller models. [12][13][14]16,20 The driving energy for the acceleration is mainly from elongated elastic cables, flowing liquids, or compressed air. ...
The principles and techniques for developing a moving model rig (MMR) driven by compressed air were introduced for moving model tests at large Reynolds numbers ( ≥ 10 6 ). A corresponding methodology for the accurate measurement of the aerodynamic drag was developed. The main functions of the MMR included the acceleration of the trailer and the model, the deceleration of the trailer, and the deceleration of the model. The acceleration power was provided by the expansion of the compressed air in a pipe, and the deceleration of the model came from the relative motion between the permanent magnet and the static iron deceleration floor. The braking of the trailer was supplied by either a magnetic damping force or the compression of the air in the pipeline by the trailer piston. The free motion of the model in the test section followed the Davis equation. Based on this, a method for the measurement of the model aerodynamic drag using the measured acceleration data was proposed and experimentally demonstrated in an MMR developed in this work.
... The complex flow field around the train, induced by the relative motion between train and ground, train and train, and train and tunnel are difficult to model using conventional static turbulence wind-tunnel experiments (Baker, 1986;Zhang et al., 2017, Zhang et al., 2019a. Comparatively, moving-model rigs are highly suitable for experimental simulation of trains passing tunnels, buildings, slipstreams, and more. ...
... The model scale 1:20 in this study meets the requirements described in CEN Standard (BS EN, 2005, 2006, that is, the test model scale shall be 1/25 or larger to ensure that Reynolds number effects are minimized. In addition, the scaled experimental Reynolds number is larger than 3.6 Â 10 5 in this study, thus, the flow field is determined to approximately satisfy the similarity criterion (Auvity and Kageyama, 1996;Auvity and Bellenoue, 2005;Dalley and Johnson, 1999;Zhang et al., 2017). In this case, the Reynolds number has little influence on the train aerodynamic characteristics (Yang et al., 2016;Bell et al., 2014), which can ensure that the tested pressure values on scaled models are representative of full scale (BS EN, 2005, 2006. ...
... Type of pressure sensor located on train and tunnel surface is Honeywell DC030NDC4, and the sampling frequency of the pressure sensor is 1 kHz (Tao et al., 2019;Lu et al., 2020). As prescribed by Zhang et al. (2017), plastic tubes were used for the connection of the probe of the differential pressure sensors and the holes drilled on the train-model surface. Photoelectric sensors were arranged at the front terminal of the noise barriers to measure train speeds when the model arrived at the front terminal of the noise barrier. ...
The pressure variations on train surfaces and noise barriers induced by a model train passing barriers of 0.125 and 0.25 m are studied using a 1/20 moving model. Pressure–time history curves on train surfaces and noise barriers are presented and compared with those of BS EN 2005. The influences of train speed, noise-barrier height, and crossing speed of trains are analyzed with their respective pressure distributions. The results indicate that the pressure amplitudes on train surfaces and noise barriers increase when the train speed and the height of the noise barrier increases, and the pressure amplitudes on the same noise barriers decrease significantly when the heights of the pressure taps increase.
... They also discussed the pressure characteristics on the train surface when the train was passing by the station and when two trains intersected at the station. Zhang et al. [32] used a 1/20 scale model to analyze the impact of differently shaped hood structures at a tunnel opening on the initial compression waves, showing that a hat oblique tunnel portal combined with a buffer structure with top holes was particularly effective. Gilbert et al. [33] made a 1/25 scale train model to study the slipstream under different blockage ratios and different tunnel lengths. ...
... To ensure that the pressure wave amplitude did not decrease, the rigid tunnel model was well sealed on the moving model test bed, allowing us to measure the transient pressure on the train surface, the transient pressure on the tunnel wall, and the slipstream in the tunnel. Before this, a series of tests, including a measurement of the pressure on the train surface, the pressure on the tunnel wall, and the pressure of the accessory device at the rail side, were performed on the moving model platform, and some reliable test results were acquired [30][31][32]. ...
... The data sampling frequency of the measurement system was 5 kHz. The data set was smoothed using a first low-pass Butterworth filter with a cut-off frequency of 0.005 s [31][32]35]. ...
In this study, the spatial distribution of the transient pressure and the slipstream caused by a 1/10 scaled metro train passing through a tunnel was studied with moving model test. We hereby investigate the mechanism underlying the mitigation of the transient pressure on both the train surface and tunnel wall, as well as that of the slipstream in the tunnel. Experimental results showed that the airshaft at different locations in a tunnel had different pressure relief effects. The most significant pressure amplitude decreased by 36.0% with the airshaft locating in the middle of the tunnel. Meanwhile, the slipstream speed was also relieved from 0.45 to 0.36 after an airshaft. We also assessed and analyzed the impact of train speed on the transient pressures and slipstream. It was found that the increase of the train speed would increase the transient pressure and slipstream speed, but it did not effect their spatial distribution.
... (i) Formation mechanism of fluctuating pressure waves [154,155]: ...
... (ii) Amplitude and time gradient of fluctuating pressure waves [147][148][149][150][151][152][153][154][155]: ...
... (v) Designing airtightness carriages to prevent the propagation of strong pressure waves from outside into the carriages [154,155,161,[165][166][167]; ...
High-speed railway aerodynamics is the key basic science for solving the bottleneck problem of high-speed railway development. This paper systematically summarizes the aerodynamic research relating to China’s high-speed railway network. Seven key research advances are comprehensively discussed, including train aerodynamic drag-reduction technology, train aerodynamic noise-reduction technology, train ventilation technology, train crossing aerodynamics, train/tunnel aerodynamics, train/climate environment aerodynamics, and train/human body aerodynamics. Seven types of railway aerodynamic test platform built by Central South University are introduced. Five major systems for a high-speed railway network—the aerodynamics theoretical system, the aerodynamic shape (train, tunnel, and so on) design system, the aerodynamics evaluation system, the 3D protection system for operational safety of the high-speed railway network, and the high-speed railway aerodynamic test/computation/analysis platform system—are also introduced. Finally, eight future development directions for the field of railway aerodynamics are proposed. For over 30 years, railway aerodynamics has been an important supporting element in the development of China’s high-speed railway network, which has also promoted the development of high-speed railway aerodynamics throughout the world.
... Examples of the damage to the train and the tunnel resulting from the aerodynamic pressure are shown in Fig. 1. Therefore, an increasing number of scholars have studied the aerodynamics of the train and tunnel through different experimental, numerical, and theoretical methods (Howe et al., 2006;Zhang et al., 2017;Gilbert et al., 2013;Liu et al., 2016). At present, the scaled moving model test and numerical simulation are the main methods used to simulate the aerodynamic effects on trains running through tunnels (Liu et al., , 2016Howe et al., 2006;Zhang et al., 2017;Gilbert et al., 2013). ...
... Therefore, an increasing number of scholars have studied the aerodynamics of the train and tunnel through different experimental, numerical, and theoretical methods (Howe et al., 2006;Zhang et al., 2017;Gilbert et al., 2013;Liu et al., 2016). At present, the scaled moving model test and numerical simulation are the main methods used to simulate the aerodynamic effects on trains running through tunnels (Liu et al., , 2016Howe et al., 2006;Zhang et al., 2017;Gilbert et al., 2013). Because of limitations of both the cost and size of test equipment, full-scale train tests are mainly conducted for verification Zhang et al., 2017;Liu et al., 2016). ...
... At present, the scaled moving model test and numerical simulation are the main methods used to simulate the aerodynamic effects on trains running through tunnels (Liu et al., , 2016Howe et al., 2006;Zhang et al., 2017;Gilbert et al., 2013). Because of limitations of both the cost and size of test equipment, full-scale train tests are mainly conducted for verification Zhang et al., 2017;Liu et al., 2016). The length of trains in the scaled train model test is short because it is restricted by the site and equipment of the test Yang et al., 2016). ...
Inthisstudy,theaerodynamicperformanceoffull-scaletrainsofdifferentlengthsgoingthroughorcrossingeach other in a tunnel was investigated using sliding mesh technology and a numerical algorithm developed and verified through a full-scale train test. The waveforms of the fluctuating pressure distribution on the train and in the tunnel were compared and analyzed, and the effect of the train length on the flow field in the tunnel examined. The results show that, because of the significant difference in pressure amplitude, long trains cannot be replaced by short trains when simulating trains going through or crossing each other in tunnels. However, some common regular patterns, such as the distribution of the peak values of the time evolution of pressure on the train and in the tunnel, can still be found in both cases. It was found that, for the evaluation of the fatigue effect induced by pressure on the train body, the equivalent load method based on the Paris formula is more secure and reliable than the root-mean-square equivalent load method. It was also discovered that, while analyzing the effect of the fluctuating aerodynamic pressure, it is better from the viewpoint of safety to consider the maximum pressure on the constant-section part of the train body as the representative parameter.
... 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. ...
... This moving model rig is comprised of three sections: the acceleration section with a length of 57 m, the test section with a length of 50 m, and the braking section with a length of 57 m. As described previously by Zhou et al. (2014) and Zhang et al. (2017), the power system for the moving model rig is located on the bottom layer, and the mechanical propulsion system is designed to accelerate the model train based on the use of a rubber rope, pulley group, and power transfer car. The train model runs on the upper layer, where the tracks and fixed measurement system are installed. ...
... According to (BS EN, 2006), when the scale is greater than 1:25, the influence of Reynolds number is minimal. Moreover, The Reynolds number in this test is greater than 3.6 × 105, which means that the similarity criterion is almost met (Dalley and Johnson, 1999;Zhang et al., 2017) Therefore, this test can reflect the pressure transients when the real train passes through the tunnel. ...
The setting of tunnel linings is an effective way to reparation tunnel damage, which can also improve the tunnel surface structure. However, increased linings will change the cross-sectional area of the tunnel, affecting the pressure transients induced by the train passing through the tunnel. In this study, the non-circular linings' influence on the pressure transients is analyzed based on moving model tests. Six distribution modes of the non-circular linings inside the tunnel are adopted for the experimental test. The characteristics of pressure transients induced by a single train passing through a tunnel are discussed and compared with the configuration without lining. The results of this experiment show that the influence of the non-circular linings distribution along the circumferential direction and the length direction is significant to a certain extent, which can guide the design of tunnel lining. These findings suggest that it is feasible to install non-circular lining in the tunnel to maintain tunnel damage, and reasonable distribution of the non-circular lining can also reduce the pressure amplitude of the initial compression wave.
... BELLENOUE et al [7] and RICCOA et al [8] studied the characteristics of pressure waves in a high-speed train tunnel based on moving model tests. ZHANG et al [9] and ENDO et al [10] studied oblique tunnel portal effect on pressure fluctuations of a high-speed train passing through a tunnel by using moving model test. ...
... For the measurement of pressure fluctuations, Honeywell DC030NDC4 pressure sensors are chosen in this test. The detailed introduction for the test platform can be found in Ref. [4,9]. ...
Calculation grid and turbulence model for numerical simulating pressure fluctuations in a high-speed train tunnel are studied through the comparison analysis of numerical simulation and moving model test. Compared the waveforms and peak-peak values of pressure fluctuations between numerical simulation and moving model test, the structured grid and the SST k-ω turbulence model are selected for numerical simulating the process of high-speed train passing through the tunnel. The largest value of pressure wave amplitudes of numerical simulation and moving model test meet each other. And the locations of the largest value of the initial compression and expansion wave amplitude of numerical simulation are in agreement with that of moving model test. The calculated pressure at the measurement point fully conforms to the propagation law of compression and expansion waves in the tunnel.
... More detailed information about the platform is provided in Refs. [30] and [31]. The air velocities were 1, 2, 3, 4, and 5 mÁs À1 . ...
... (Detailed information about the platform can be found in Refs. [30,31].) The real subway car used for the experiment had the dimensions shown in Fig. 1(a). ...
The internal flow field study of car compartments is an important step in railroad vehicle design and optimization. The flow field profile has a significant impact on the temperature distribution and passenger comfort level. Experimental studies on flow field can yield accurate results but carry a high time and computational cost. In contrast, the numerical simulation method can yield an internal flow field profile in less time than an experimental study. This study aims to improve the computational efficiency of numerical simulation by adapting two simplified models—the porous media model and the porous jump face model—to study the internal flow field of a railroad car compartment. The results provided by both simplified models are compared with the original numerical simulation model and with experimental data. Based on the results, the porous media model has a better agreement with the original model and with the experimental results. The flow field parameters (temperature and velocity) of the porous media model have relatively small numerical errors, with a maximum numerical error of 4.7%. The difference between the numerical results of the original model and those of the porous media model is less than 1%. By replacing the original numerical simulation model with the porous media model, the flow field of subway car compartments can be calculated with a reduction of about 25% in computing resources, while maintaining good accuracy.
... Johnson and Dalley 29 have conducted 1/25th scaled experiments for a passenger train passing through a tunnel at the TRAIN Rig, and the comparison of pressures inside the tunnel with full-scale results showed excellent agreement. Similar experiments to the current study have been 30 using a scaled moving model. The pressure amplitudes do not change in full scale, but the pressure traces in the scaled tunnel occur 25 times faster than in full scale. ...
... When conducting scaled tests on trains in tunnels with Re>360,000, the similarity criterion is satisfied. 13,[30][31][32][33] Mach number is a similarity parameter for the compressibility of the air. According to CEN, the fullscale Mach number must be respected for speeds up to 0.3, although the characteristic length changes. ...
The objective of this study was to investigate the aerodynamic effects of a freight train passing through a tunnel. The nose entry generates a complex pattern of reflective pressure waves (piston effect) which can lead to intense aerodynamic forces. Previous research on the topic has focused on passenger trains because of higher speeds. The experiments of this study use a 1/25th scaled moving model at the TRAIN Rig at a speed of 33.5 m/s with a blockage ratio of 0.202. The monitored pressure along the tunnel wall can increase up to almost 1000 Pa because of the initial compression wave, while it drops when an expansion wave or the tail passes by. The maximum pressure is observed at the train nose due to air stagnation (1500 Pa) where the flow is steady, while the roof and sides experience negative pressures due to unsteady flow separation. The effect of loading configuration is significant as partially loaded trains can create a second pressure peak on the tunnel walls (after the initial compression wave) and affect the flow at the tunnel entrance wall. Under the current testing conditions, the results indicated compliance with the requirements of the Technical Specification for Interoperability and a constant pressure gradient of the initial compression wave which is in contrast with the passenger train's two-part gradient. Further work on the topic could provide visual information about the exiting jet towards the portal and the separation bubble around the train.
... The lengths of the train and the tunnel can affect the interval time between the propagating pressure waves in the tunnel, thus subsequently affecting the shape and amplitude of pressure transients (Ricco, Baron, & Molteni, 2007). The nose shape of the train (Kikuchi, Iida, & Fukuda, 2011) and the tunnel hood (Uystepruyst, William-Louis, & Monnoyer, 2013;Zhang, Yang, Liang, & Zhang, 2017;) can affect the generation of the pressure waves, thereby subsequently impacting the pressure transients and the micropressure wave. Further, the airshaft (Miyachi, Fukuda, & Saito, 2014), cross passage (Li, Liang, & Zhang, 2010), and side branch (Fukuda, Ozawa, Iida, Takasaki, & Wakabayashi, 2006) can change the pressure transients owing to the dispersion and reflection of the pressure waves in these structures. ...
... To simulate the pressure transients induced by a train passing through a tunnel, a three-dimensional, unsteady, and turbulent model was applied. The primary governing equations are continuity, momentum, energy, and turbulence; for more details of the governing equations, see Liu et al. (2010) and Zhang et al. (2017). ...
... 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.
... This test was performed at the Central South University in China. Zhang et al. [41] had provided detailed information about the experiment. Two 1/16th-scale MTs with two-car marshalling for each train were adopted, and the trains met at an equal speed of 200 km/h for each train. ...
The strong change in the flow fields around two maglev trains (MTs) passing each other in open air may affect their manoeuvrability and passengers’ comfort. In this study, we evaluated the aerodynamic performance of two MTs passing each other via shear stress transport (SST) k–ω model and improved delayed detached eddy simulations based on the Spalart–Allmaras model (SA−IDDES) and the SST k–ω model (SST−IDDES). The accuracy of the numerical simulation method was verified using experimental data acquired from a moving model test. The results showed that the difference in the amplitude of the transient pressure obtained with the different turbulence models was less than 5%. The wake vortex structures on the intersection side were found to interact, and their intensity consequently decreased. The SST−IDDES model produced smaller-scale vortices than the SA−IDDES model, particularly in the near-wake region. There were large differences in the drag and lift forces obtained using the different turbulence models. Among them, the lift force of the tail car was more sensitive to the turbulence model, and its maximum value obtained with the SST−IDDES model was 11% larger than that obtained with the SA−IDDES model.
... CHEN et al [8] and ZHOU et al [9] studied the impact of ambient wind on the pressure variations when two trains intersect inside a tunnel and a train passes through a tunnel, and they obtained the significant findings that the positive pressure on the train surface increases and the negative pressure decreases as the wind velocity increases when the train is traveling downwind. Other studies have addressed micro-pressure waves (MPWs) and mitigation measures, interior pressure change and so on [10][11][12][13][14][15]. ...
The transient pressures induced by trains passing through a tunnel and their impact on the structural safety of the tunnel lining were numerically analyzed. The results show that the pressure change increases rapidly along the tunnel length, and the maximum value is observed at around 200 m from the entrance, while the maximum pressure amplitude is detected at 250 m from the entrance when two trains meeting in a double-track tunnel. The maximum peak pressure on the tunnel induced by a train passes through a 70 m2 single-track tunnel, 100 m2 double-track tunnel and two trains meeting in the 100 m2 double-track tunnel at 350 km/h, are -4544Pa, -3137Pa and -5909Pa, respectively. The
aerodynamic pressure induced axial forces acting on the tunnel lining are only 8%, 5% and 9%, respectively, of those generated by the earth pressure. It seems that the aerodynamic loads exert little underlying influence on the static strength safety of the tunnel lining providing that the existing cracks and defects are not considered.
... Besides, there are 279 subway lines 34 under construction nationwide, with a total length of 6,902.5 kilometers. 35 When the train enters the tunnel, the internal air will be strongly squeezed by the train due to the 36 closed space of the subway tunnel, and the gas at the tunnel entrance will be compressed, which leads 37 to rapidly rising pressure, forming a pressure pulse [1][2]. As is shown in Fig 1, the phenomenon 38 when the pressure pulse travels along the tunnel at speed close to that of sound is called compression tunnel [18][19]. ...
The pressure wave is of crucial importance for subway development since it greatly influences the comfort while taking. 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 paper, 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. Still, it also increases the negative pressure amplitude when the train passes.
... Train aerodynamics is, in fact, a broad subject which considers several aspects and topics. To name a few, shape optimization (Krajnović, 2009;Li et al., 2016), cross wind effects (Hongqi, 2015;Baker, 2013;Zhang et al., 2018;Cheli et al., 2010;Liu et al., 2016;Zhang et al., 2017a), pressure variation when train running through tunnels Chen et al., 2017a,b;Khayrullina et al., 2015;Zhang et al., 2017b), slipstreams investigations (Baker et al., 2014a,b;Bell et al., 2015Bell et al., , 2016aRocchi et al., 2018;Huang et al., 2016), underbody flow study (Quinn et al., 2010;Jönsson et al., 2014;Paz et al., 2017) and ground effect Xia et al., 2015Xia et al., , 2017Wang et al., 2018a,b) are just part of the vast literature generated on the this topic by various research groups in the last decade. ...
The influence of ground clearance on the flow around a simplified high-speed train is investigated in this paper. Four clearance heights are studied using IDDES. After a grid independence study, the results of the simulations are validated against experimental data present in the literature. It is found that the drag decreases when reducing the clearance gap from the baseline height to a possibly critical height, while drag remains constant when the clearance is lower than this critical height. The negative lift (downforce) increases with the decreasing of the clearance gap. The flow is particularly influenced by the gap height at the underbody and wake regions, where a lower underbody velocity and a higher wake velocity are observed with lower clearance down to case h2. Therefore, the different topologies of the wake are presented and described. Particular attention is paid to the description of the wake flow and to the position and the formation of the flow mixing region. Specifically, with decreasing clearance, the mix of the tail downwash and underbody flows happen earlier, and the core of the counter- rotating vortices in the wake tends to develop with an increasing height trend. Overall, aerodynamic performance and flow structure descriptions show positive and negative effects when decreasing gap clearances, which should be taken into account for new design strategies.
... (Chen et al., 2017;EN 14067-4. 2009) Thus, height of the domain should be no less than 10 times of the characteristic height (h) of the computational model, and the width of the domain should be no less than 20 times of the computational model (Chen et al., 2017;Zhang et al., 2017a). ...
... However, these tests were associated with drawbacks (mainly costs) that led to the development of moving model facilities operating in air (Baker 1986;Pope 1991). Especially when considering Mach numberdependent tunnel effects, which have been studied intensively using moving models (Howe et al. 2003;Heine and Ehrenfried 2012;Zhang et al. 2017), air appeared to be the more practical working fluid. Also in the field of road vehicle aerodynamics, despite the attempts to draw more attention to towing tank testing by Erickson et al. (1986) and Gad-el Hak (1987), only few such investigations have been performed over the last decades (Aoki et al. 1992;Larsson et al. 1989;Stephens et al. 2016;Schmidt et al. 2017). ...
The present study assesses the applicability of towing tank experiments using a moving model for the investigation of the aerodynamics of long land-borne heavy vehicles such as buses, trucks, and trains. Based on experiments with a 1:22 scaled model of a high-speed train, the influence of various conditions relevant for the transferability of the results obtained in water to air is analysed exemplarily. These conditions include surface waves, cavitation and submergence depth. The experiments were carried out in the shallow water towing tank of the Technische Universität Berlin. It is shown that outside a critical Froude number range of about 0.2 < Fr < 1.2 the impact of the surface waves can be neglected and no cavitation appears in the velocity range investigated. Furthermore, a correction method is proposed taking into account the bias through surface waves at small submergence and thus allowing for a wider Froude number range. The data obtained in the towing tank are found to be in excellent agreement to other investigation methods.
Graphical abstract
... Except for internal structures of a tunnel, the tunnel portal has also been the research objective in an improvement of pressure pattern. The influence of different opening structures at the tunnel entrance was investigated by Howe (1999) and Zhang et al. (2017). The former concentrated on compression wave formation and reported that the rise time of the compression wave generated by the entry of a train could be elongated by 'venting' the tunnel to relieve the initial build-up of the pressure caused by the entering train; the latter applied a moving model experiment to investigate shapes of tunnel portals with considering transient pressure and micro-pressure waves of train's tunnel operation, they finally found a hat oblique tunnel portal combined with a buffer structure and top holes was particularly effective. ...
... ZHOU [7], LIU et al [8], DANIEL et al [9] and ZHOU et al [10] numerically studied pressure transients in high-speed trains passing through tunnels of different tunnel parameters. In order to reduce the pressure transients, YANG et al [11] and ZHANG et al [12] studied oblique tunnel portal effect on pressure transients of high-speed train passing through a tunnel. LI et al [13,14] studied the effect of auxiliary structures, such as cross passage and shaft, on pressure transients in a tunnel. ...
The influence of enlarged section parameters on pressure transients of high-speed train passing through a tunnel was investigated by numerical simulation. The calculation results obtained by the structured and unstructured grid and the experimental results of smooth wall tunnel were verified. Numerical simulation studies were conducted on three tunnel enlarged section parameters, the enlarged section distribution along circumferential direction, the enlarged section area and the enlarged section distribution along tunnel length direction. The calculation results show that the influence of the different enlarged section distributions along tunnel circumferential direction on pressure transients in the tunnel is basically consistent. There is an optimal enlarged section area for the minimum value of the pressure variation amplitude and the average pressure variation in the tunnel. The law of the pressure variation amplitude and the average pressure variation of the enlarged section distribution along tunnel length direction are obtained.
... (i) decreasing the compression wave gradient during its formation by constructing a hood at the tunnel entrance, which may be a flared [5,6], inclined [7][8][9], section-enlarged [10][11][12], vented [12][13][14] hood, or complex hood composed of a combination of those simple structures [15], as illustrated in the schematic shown in Fig. 1; ...
Micro-pressure waves are a major environmental problem related to modern high-speed railway systems. The strength of this harmful noise is proportional to the amplitude of the compression wave gradient generated by a high-speed train entering a tunnel. Employing an accurate numerical method, the mechanism and effects of ventilation openings on these compression waves are parametrically investigated. The numerical results indicate that after installing an opening, the compression wave is principally developed as multiple series of wave families, and thus, the pressure gradient curve is formed by numerous peaks and troughs. The gradient peaks UP0 and UV0 are generated successively by the train nose entering the tunnel and passing over the opening, respectively, and dominate the maximum pressure gradient. The vent ratio of the opening can be optimized by balancing these two peaks. However, the vent location and train Mach number can significantly affect the optimizing and the aerodynamic behaviour of the optimized opening, which is attributed to wave superposition. Three original engineering equations are proposed for understanding the effects of the vent ratio, vent location and train Mach number on the gradient peaks, respectively, and the denoising capability of the opening is evaluated.
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.
The pressure comfort of a high-speed train is closely related to the static and dynamic airtightness performance of the train carriage, and this performance is studied mainly with field surveys and tests on full-scale trains. Considering the high cost and difficulty of full-scale tests, the applicability of the reduced-scale model experiment method in the study of train carriage airtightness performance is worth exploring. In this study, a power–law relationship between the scale factors and static airtightness coefficients of carriage models was first established using numerical simulations, to determine the fundamental theoretical support for a reduced-scale model experiment in the study of train airtightness performance. A series of static and moving model experiments were conducted on a newly designed 1/20th-scale special train carriage model. The static airtightness coefficients obtained from static model experiments showed a discrepancy less than 5% to their theoretical values, which revealed the experimental feasibility of the reduced-scale model for studying the static airtightness performance. The pressure spectrum characteristics of the measured pressure from the moving model experiment indicated that not only the high-intensity aerodynamic alternating pressure load with a frequency peak around St = 1.76 but also the high-frequency mechanical vibrations around St = 17.03 from the wheel-rail coupling system were experienced by the carriage body traveling through a tunnel, which might cause some potential leakages to appear on the carriage body. This provides a new understanding of the potential causes of the deterioration of the train’s dynamic airtightness performance. These works and findings provide new insights and reference cases for studying the static and dynamic airtightness performance of a train carriage with the method of reduced-scale model experiments.
Wind tunnel tests have been widely applied in aerodynamic investigations owing to their unique advantages. However, it is difficult to theoretically establish a simplified symmetry or two-dimensional model because of the relative motion of the structures and proximity of the train to the ground/infrastructure. Additionally, railway-related aerodynamic problems tend to be more challenging than those encountered in other engineering structures. Moreover, transient and crosswind effects, as well as complex operation environments, need to be considered, thereby making aerodynamic analyses of train–bridge systems challenging. Advanced manufacturing methodologies can reproduce realistic scenarios of high-speed train (HST) operations in a wind tunnel. The development of a controllable and affordable experimental method presents considerable research opportunities and challenges. There exists a strong correlation between wind tunnel experimental methods and the understanding of aerodynamic mechanisms, and some wind tunnel tests are dedicated to identifying the aerodynamic behavior using specific test systems. This study mainly describes the types of tests typically performed in a wind tunnel to analyze the aerodynamic issues of train–bridge systems under wind action. To identify and understand the individual role of the above mentioned-correlated systems, trains and bridges in wind tunnel tests are described separately. High-speed trains on bridges must be made safe and environmentally friendly, and a few cases are presented as indications to reconsider our aerodynamic research priorities. Thus, advanced experimental activities have been proposed in the Central South University (CSU) wind tunnel, representing helpful practices in defining the real-world aerodynamic behavior of wind-vehicle-bridge systems.
The train-induced airflow in a railway tunnel is of great significance for tunnel ventilation, fire rescue, and ancillary facilities overall. Previous research mainly focused on piston wind in metro tunnels, while the slipstream in high-speed railway tunnels is more drastic and complicated owing to the faster vehicle speed and diverse blockage ratios. In this research, a computational fluid dynamics (CFD) study was carried out to explore the three-dimensional transient airflow induced by a commercial high-speed train circulating through tunnels at 350 km/h under different blockage ratios (β = 0.175, 0.160, 0.140, 0.122, and 0.112). First, the train-tunnel model was established based on the unsteady Reynolds-Averaged Navier–Stokes (URANS) method merged with the sliding mesh technique, altogether validated with experimental evidence. Then, the resultant slipstream and the individual components were investigated, and it was concluded that the longitudinal component was dominant. The variation behaviors of the slipstream and local pressure with the different blockage ratios were comparatively obtained. Finally, the relationships between the slipstream and the spatial distance in longitudinal, lateral, and vertical directions were analyzed. This study provides a guideline for the determination of the tunnel clearance, and wind load evaluation in a high-speed railway tunnel.
Micro-pressure waves (MPWs) emitting from the exit of a railway tunnel pose a serious environmental hazard causing vibration and rattling of nearby structures. Consequently, with the advent of ever increasing train speeds, it has become extremely important for tunnel engineers and designers to control the emission of MPWs from the exit of a railway tunnel. The most economical and effective method known till date to reduce the magnitude of MPWs is by installing an aerodynamic hood at the entrance of a tunnel. Therefore, a newly designed entrance hood with air-slits attached on each side is studied in the current work. The air-slits are designed to bio-mimic the ‘ram ventilation’ technique used for respiration by hunter shark gills. These air-slits reduce the maximum value of the pressure gradient of the compression wave generated near the entrance. Thereby, a subsequent reduction in the maximum magnitude of MPWs emitted from the exit of tunnel is observed. A prototype of this entrance hood has been employed on a 1/64.2 reduced scale single track model tunnel and experimental tests were conducted using a model train with the nose shape of EMU-250 at two entry speeds of 180 km/hr. and 250 km/hr.. Pressure on the tunnel wall were measured at six different locations using a piezo-resistive pressure transducer and MPW at the tunnel exit were captured at three locations using a low-frequency sound level meter. A reduction in the pressure gradient of the compression wave and magnitude of MPW of about 56.3% and 78.7% respectively was observed with the installation of this entrance hood at a train speed of 250 km/hr. The obtained pressure transient data and the corresponding MPW values for both the train speeds are presented in detail with clear elucidations on the flow phenomena. Further, an analytical model to predict MPWs was developed using the solution of a vibrating circular piston in an infinite baffle plate. The predicted results of the analytical model when compared with the experimental values show a reasonably good match for the peak pressure magnitude and waveform of the MPW.
The main aim of this investigation is to analyse the flow around a freight train as it passes through a tunnel. The separated flow around the train nose is related to energy losses, lateral vibration, noise and streamline deviation, and it also influences the velocity magnitudes around the train. Such effects are expected to become more important with the prospect of increasing freight train speeds. The numerical simulations performed in this study use a Class 66 locomotive connected to eight container wagons, scaled to 1/25th, moving at a train speed of 33.5 m/s through a tunnel with a blockage ratio of 0.202. The k–ω model combined with a high advection scheme solves the governing equations on a structured hexahedral mesh using the sliding mesh technique. The pressure histories at the tunnel walls and train surface as well as the velocity field around the train were validated with experimental data obtained using a moving model. The longest separation bubble is found at the middle-height and middle-width of the locomotive due to extended corners at these regions. When the train enters the tunnel, the separation length is reduced by 32% at the roof and 31% at the sides, compared to open air. The maximum separation length is found at the sides of the train where it reattaches at 19% of the locomotive length, influencing the velocity peak at a short distance from the train surface. The larger the separation length, the higher the length/duration of this peak. When the train head is halfway through the tunnel, the nose velocity peak reduces by 30% compared to open air. The position of the nose inside the tunnel affects not only the slipstream velocity but also the velocity field at the tunnel portal and exit. These novel findings can be used as a benchmark for designing new freight train and tunnel shapes.
The coupling and complexity of railway train / tunnel system are further aggravated by increasing train speed, which produces a series of aerodynamics problems, such as aerodynamic drag, slipstream, pressure wave and micro pressure wave. Aerodynamic effects of tunnels will result in a significant increase in train energy consumption, shorten life of railway train / tunnel system, and increase maintenance cost. This paper provides a review of aerodynamics of railway train / tunnel system. Challenges in railway train / tunnel system aerodynamics and their related factors are discussed firstly. Aerodynamic performance and flow field characteristics of trains in tunnels are presented. Relationship of aerodynamic effects and parameters of railway train / tunnel system, and the control methods for reducing aerodynamic effects in tunnels are explained. A traffic safety evaluation of the train in tunnels, such as vehicle body structure, passengers’ ear comfort, etc., is introduced and analysed. Finally, future outlooks and research topics are proposed.
The aerodynamic loads on the overhead bridge bottom surface induced by train passage are reported in this paper. Both moving model test and numerical simulation approaches at the 1:20 scale are used. The numerical work is validated through both mesh independence tests and comparison with experimental data. Typical pressure variation curves are plotted and compared with previous studies. The peak pressure values’ dependence on the Reynolds number is considered through four sets of experiments with different train running speeds. The peak pressure coefficient distribution law for the bridge bottom surface is presented. Differences in the pressure distribution in different bridge bottom areas are explained based on more detailed flow field information. The influence of the bridge height on the aerodynamic load magnitude and time interval is presented. Moreover, the application of the CEN Standard to practical engineering issues is discussed.
Alleviation of the pressure transients caused by high-speed trains intersecting in a tunnel with partially reduced cross-section is investigated by numerical simulation. The RNG k-ε turbulence model and hybrid grid are adopted for the numerical simulation, which is validated by the moving model test. Two factors, the length of reduced section (L) and the train marshalling number, are considered to analyse the alleviation effect. The results show that, for reduction of the pressure transients induced by the intersection of three-car marshalling trains, the location of the change in cross-section is supposed to be near the location of the maximum value of the initial expansion wave (L → 240 m). In addition, for four-car marshalling trains intersecting in a tunnel of L = 240 m, the excavation volume of the tunnel (tunnel volume) decreases by 14.4%, and the average pressure amplitude on the train surface decreases by 7.9%. Especially the pressure amplitude at the measurement point in the streamlined area of the tail car decreased by 28.6%. The reduced section tunnel has a good effect on decreasing the pressure transients around train body and the tunnel excavation volume (construction cost), which helps the tunnel design process.
A moving model test was carried out to investigate the associated smoke movement characteristics when a subway train on fire runs in a tunnel. Train models of the 1/10 and 1/15 scales were used. The spatial distributions of airflow velocity and smoke concentration were then analyzed, and the differences between moving fire sources and stationary fire sources were discussed. The results show that the smoke movement characteristics of a stationary fire source were greatly different from those of a moving one. Specifically, the smoke movement for the moving fire source was dominated by piston wind. Moreover, the process of the smoke spread could be divided into three stages, during which time the flow direction changed. The peak smoke concentration value occurred after the train tail passed by the measuring point. Besides, the impacts of train speed (60 km/h, 80 km/h, 100 km/h, and 120 km/h) and blockage ratio (0.19 and 0.43) on airflow velocity and smoke concentration were also investigated. With increasing train velocity, the airflow velocity increased, and the smoke concentration decreased. The maximum airflow velocity was approximately linear with the train velocity. Furthermore, the increasing blockage ratio enhanced the piston effect in the tunnel, thus increasing the airflow velocity and reducing the smoke concentration.
Using a 1:20 scale moving model device, pressure distributions on train and tunnel surfaces, and the distribution of micro-pressure waves within 50 m of tunnel exits were investigated. In addition, the effects of train speeds on the transient pressures and micro-pressure waves were analyzed. The results revealed that the effect of the train speed on Pmin values was more significant than that on Pmax values, on the train surface. Significant differences between symmetrical measurement points located on the same cross section of the tunnel with double tracks could be observed. Moreover, similar differences between symmetrical points located on the same cross section in the streamlined zone of the model train were observed and analyzed. The pressure changes in the measurement points located on the same cross section of the train body, other than the streamlined zone, were approximately coincident. The differences between the Pmin values of measurement points located on different cross sections of the tunnel determined the differences between the ΔP values of these measurement points. The micro-pressure waves were approximately equal for measurement points located on the same cross section. Moreover, linearity decreased when the distance between the measurement points and the tunnel exit increased.
Pressure gradient and micro-pressure wave induced by a high-speed train entering a tunnel were investigated for the parametric design of equal-transect oblique tunnel portal. A moving model experimental test was conducted to verify the computational method and mesh. The influence of three main factors (portal shape, slope value, and aperture ratio) of the equal-transect oblique tunnel portal were considered in this study. The results showed that the hat oblique shape was the most efficient portal design to alleviate the pressure gradient and micro-pressure wave compared to the other designs examined in this study, and the mitigation mechanism of the hat oblique design on the initial compression wave was explained. Then the effects of the slope value and the aperture ratio of hat oblique tunnel portal on the pressure gradient and micro-pressure wave were investigated, and the parameters of the equal-transect oblique tunnel portal were optimized to alleviate the pressure gradient and micro-pressure wave induced by high-speed trains entering tunnels.
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.
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.
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.
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.
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.
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.