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The slipstreams induced by high-speed trains under crosswind are studied in this paper by the detached-eddy simulation (DES) method. First, the formation and development of the slipstream induced by a train (5 cars) with a 4 m nose length are analysed in detail, including at different heights and widths on the windward side (WWS) and leeward side (LWS). Then, the slipstreams with and without crosswind are compared, and the differences are presented. Finally, by considering four different nose lengths (4, 7, 9, and 12 m) under crosswind, the differences in the slipstreams induced by different nose lengths are given and analysed. The results show that on the WWS at z = 0.5 m above the top of the rail (TOR), the slipstream velocity coefficient ' U ' decreases at the position of the nose due to a velocity cancellation and stagnation effect. On the LWS, from D = 0 m–145 m, where 'D' represents the distance from the nose point, at y = 1.9 m and 2.15 m beside the centre of rail (COR), there are two peak values at the position of the nose caused by the impact of the nose point and the strong disturbance of the bogie area. At y = 2.65 m and 3.65 m, the change in U is relatively complex due to the effect of vortexes on the LWS. The effect of crosswind on the slipstream velocity is different in different regions around the train. In the region close to the train side and the bottom, the value of U on the WWS is the smallest, followed by that in the no wind case, and that on the LWS is the largest. In other regions, the values of U on the WWS and LWS are larger than that in the no wind case. For different nose lengths, on the WWS, the change in U is smoother with increasing nose length due to more stable flow around the nose. On the LWS, the change in U with increasing nose length is relatively clear only at the positions around the nose of the head car and tail car. In the regions along the middle cars, the U values for trains with different nose lengths change with the same trends and vary intertwined. • The formation and development of the slipstream velocity induced by a high-speed train under crosswind are investigated. • The effects of nose length on the slipstream are concluded by considering four different nose lengths—4, 7, 9, and 12 ​m. • On the LWS, the change of slipstream with increasing nose length is relatively clear only at the position around the nose. [ABSTRACT FROM AUTHOR]

Highlights • Impact of marshalling length and form on the pressure propagation was studied by Mach diagrams. • Effects of the coupling structure on the surface pressure of the train body and the tunnel wall. • The influence of marshalling parameters on the maximum pressure peak of tunnel wall and train body. • The pressure changes at the coupling structure was analysed. Abstract Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations were performed to simulate trains with different marshalling forms and lengths entering a tunnel. Three models, including a short train, a double train and a long train, were used to analyse the influence of the train configuration on the pressure variations during a train's passage. The results of the numerical predictions were validated against existing experimental data, with which they showed good agreement. The differences in the maximum pressure peak distribution and the pressure fluctuations were analysed by means of Mach diagrams. The results show that the grouping length exerts a considerable influence on the amplitude of the pressure on the train body and that the influence of the grouping length on the pressure variation on the tunnel wall varies with the location in the tunnel. The tunnel space can be divided into three and four zones with regard to the influences on the maximum positive and negative pressure values, respectively. The different marshalling forms also influence the maximum peak values and local profiles of the pressure history curves, although this influence is much slighter than that of the train's grouping length. [ABSTRACT FROM AUTHOR]

As a high-speed train passes through a tunnel, the intense aerodynamic pressure wave outside the train penetrates into the passenger compartments, changing the pressure environment inside the train and causing discomfort to passengers. This phenomenon varies enormously among tunnels of different lengths. To evaluate the real influence of tunnel length on the interior pressure environment of the carriages and ensure passenger comfort, field measurements were conducted on a CRH2A train operating on the Hefei-Wuhan rail line in China; twelve tunnels with lengths ranging from 72 to 10766 m were investigated. Pressure sensors were deployed along the outside and inside train surfaces to investigate the variations in interior pressure with the exterior pressure environment. The results show that the interior pressure curve over time in a short tunnel has a single-trough form, very different from that in a long tunnel. The total variation of interior pressure increases monotonically with tunnel length from 72 to 10766 m, whereas the maximum pressure variation within a 3 s period occurs in the 1080 m tunnel; the variation within a 1 s period is not significantly affected by the tunnel length for tunnel lengths greater than 556 m. There is a delay in the 1 s interior pressure variation in response to an exterior pressure change; this delay is independent of the tunnel length and is approximately 1.2 s in this test. It is found that the reason for passengers’ ear discomfort in very long tunnels, which is mainly an effect of excessive changes in pressure over a long period of time, could be different from that in long or short tunnels. [ABSTRACT FROM AUTHOR]

Using compressible, unsteady and sliding meshing technologies, the aerodynamic loads including transient pressure, lateral force, and overturning moment that are caused by a single train moving through a double-track tunnel or two trains passing each other in a tunnel were calculated. The dynamic response generated by applying these loads to a train body was also analysed. The results show a large difference in the pressure on both sides of the vehicle nose when a single train moves through a double-track tunnel and when two trains pass each other in a tunnel. The pressures at the symmetric measuring points on both sides of the middle of the train body are approximately the same except at the moment of passing. When the train passes the measuring points, the pressure change at the symmetric measuring points on the tunnel wall closer to the train is obviously larger than that farther from the train; the pressure changes are approximately the same at all other times. Therefore, the propagation of the pressure wave in the tunnel has good one-dimensional characteristics. Under dynamic loads in the tunnel, especially those generated by two trains passing each other in the tunnel, the lateral and vertical displacements of the underframe and side walls all increase significantly. The lateral acceleration on the roof is significantly greater than that of the underframe, which has a rolling movement below the centre of gravity. For the measuring points on both the side wall and underframe, the vertical accelerations at both ends are larger than that in the middle of the body because of a pitching motion. The horizontal and vertical vibration acceleration for a train passing another train in a tunnel are 33.8% and 47.2% larger than those for a train operating in open air, respectively. [ABSTRACT FROM AUTHOR]

In order to determine the effect of the coupling region on train aerodynamic performance, and how the coupling region affects aerodynamic performance of the couple multiple units trains when they both run and pass each other in open air, the entrance of two such trains into a tunnel and their passing each other in the tunnel was simulated in Fluent 14.0. The numerical algorithm employed in this study was verified by the data of scaled and full-scale train tests, and the difference lies within an acceptable range. The results demonstrate that the distribution of aerodynamic forces on the train cars is altered by the coupling region; however, the coupling region has marginal effect on the drag and lateral force on the whole train under crosswind, and the lateral force on the train cars is more sensitive to couple multiple units compared to the other two force coefficients. It is also determined that the component of the coupling region increases the fluctuation of aerodynamic coefficients for each train car under crosswind. Affected by the coupling region, a positive pressure pulse was introduced in the alternating pressure produced by trains passing by each other in the open air, and the amplitude of the alternating pressure was decreased by the coupling region. The amplitude of the alternating pressure on the train or on the tunnel was significantly decreased by the coupling region of the train. This phenomenon did not alter the distribution law of pressure on the train and tunnel; moreover, the effect of the coupling region on trains passing by each other in the tunnel is stronger than that on a single train passing through the tunnel. [ABSTRACT FROM PUBLISHER]

To reduce the aerodynamic drag of high-speed trains, this work proposes an air blowing configuration on the head and tail cars of high-speed trains. The variation in the aerodynamic drag and slipstream velocity is analyzed under different blowing velocities, and the flow mechanism for train aerodynamic performance alteration is explained. The results show that under the blowing speeds of U b = 0.05 U t , 0.10 U t , 0.15 U t , and 0.20 U t , where U t is the train speed, the total drag coefficient (C d) decreases by 5.81%, 10.78%, 13.70%, and 15.43% compared to the without-blowing case, respectively. However, with the increase in the blowing speed, the reduction trend of C d tends to be smoother; namely, the decrement ratio compared to the previous blowing speed for the head car is 9.08%, 0.11%, 0.60%, and 1.14% for U b = 0.05 U t , 0.10 U t , 0.15 U t , and 0.20 U t , respectively. The blowing measure generates an air gap between the coming flow and train surface, consequently causing a reduction in the viscous and pressure drag. In addition, the structure size and strength of the wake flow under different blowing cases show a decreasing trend from U b = 0.00 U t to 0.10 U t and then an increasing trend from U b = 0.10 U t to 0.20 U t. Thus, considering the blowing cost, efficiency, and flow structure evolution comprehensively, the case of U b = 0.10 U t is recommended. Under this blowing speed, the reduction ratio of the aerodynamic drag is 9.18%, 12.77%, 10.90%, and 10.78% for the head, middle, tail car, and total train, respectively. • A unique active air blowing design to reduce the aerodynamic drag of high-speed trains. • Significant reduction of the pressure drag on head middle, and tail cars by the proposed approach. • The obtained optimal blowing speed is 0.10 U t (U t is the train speed) with consideration of the blowing cost and efficiency. • Under the optimal blowing speed, the train's overall aerodynamic drag coefficient is reduced by 10.78%. [ABSTRACT FROM AUTHOR]

With an increase in train speed, the aerodynamic effects caused by the train could escalate, especially for a train running in a tunnel. A number of large transient pressure waves are generated owing to the confined spaces within the tunnel, resulting in possible damage to the vehicle structure and the facilities in the tunnel. Therefore, it is necessary to study the aerodynamic performance of a train running in a tunnel. A scaled moving model test system was constructed to facilitate the simulation of the aerodynamic effects caused by a train running in a tunnel. In this study, the influence of grid density, calculation time step, and turbulence model on the pressure caused by the train entering the tunnel was analyzed, which is helpful for choosing suitable values of the aforementioned parameters to simulate the aerodynamic performance of the train in the tunnel. The impacts of Reynolds number effect on the distribution of the surface pressure and peak of pressure wave along the train, and the pressure waveform were also studied through numerical simulation on three scaled model trains (full scale, 1/8, 1/20, and 1/32 scaled). The findings aid in understanding the relationship between the Reynolds and pressure amplitude, and the results of the scaled test can be applied to a full-scale train. [ABSTRACT FROM AUTHOR]

Transient aerodynamic pressures induced by the passage of high-speed trains past noise barriers can result in noise barrier damage. This issue is investigated experimentally in the present study by applying pressure sensors to measure the transient aerodynamic pressures acting on the inner surface (close to the railway track) of a 2.15-m high straight-type noise barrier arising from the passage of two different full-scale high-speed trains with different streamlined head cars operating at a speed of 380–420 ​km/h. The results demonstrate that the amplitudes of transient aerodynamic pressures acting on the inner surface of the noise barrier are greatest at the bottom of the noise barrier, and the pressure decreases with increasing height along the barrier. In addition, the dynamic characteristics of the aerodynamic loads are investigated using the fast Fourier transform algorithm. The main frequencies of the transient aerodynamic pressures observed over the train speed range considered are found to be proportional to the train speed and inversely proportional to the single-car length. Moreover, the results of analysis indicate that noise barrier damage can be minimized over the train speed range considered by building noise barriers with natural frequencies residing outside of the 4.21–4.74 ​Hz range. • Full-scale experiment about transient pressure on noise barrier induced by high-speed trains running at 380–420 km/h. • The amplitudes characteristics of transient aerodynamic pressures acting on the surface of the noise barrier. • The main frequencies of the transient aerodynamic pressures at different train speed. [ABSTRACT FROM AUTHOR]