High-speed Railway Tunnel Research Articles

Sound propagation in long enclosures with a vertical or inclined branch

It is of interest to investigate the sound propagation in long enclosures with a vertical/inclined branch, since this may be relevant to long enclosures in practical applications, such as in high-speed railway tunnels. However, much research on sound propagation in long enclosures available is concerned with straight long enclosures. In this paper, the sound pressure level (SPL) attenuation, early decay time (EDT), and reverberation time (RT30) of long enclosures with vertical/inclined branches have been studied by comparing experimental results from physical scale models, of such enclosures with those for a straight long enclosure. It has been found that, compared with the straight long enclosure, the inclined branch makes more-difference to the SPL, EDT and RT30 of the long enclosure than the vertical branch, even though both kinds of branches have the equivalent volume.

高速鉄道用トンネルから発生する微気圧波の低減に関する研究(圧縮性流体の基礎と応用技術 OS.4)

高速鉄道用トンネルから発生する微気圧波の低減に関する研究(圧縮性流体の基礎と応用技術 OS.4)

615 高速鉄道トンネル内を伝播する圧力波のパッシブコントロール

615 高速鉄道トンネル内を伝播する圧力波のパッシブコントロール

Numerical study of compression waves passing through two-continuous ducts

In order to investigate the impulsive noise at the exit of high-speed railway tunnel and the pressure transients inside the tunnel, numerical calculations using a Total Variation Dimishing difference scheme were applied to axisymmetric unsteady compressible flow field. Some compression wave forms were assumed to model the compression wave produced in real high-speed railway tunnel. The numerical data were extensively explored to analyze the peak over-pressure and maximum pressure gradient in the pressure wavefront. The effect of the distance and cross-sectional area ratio between two-continuous ducts on the characteristics of the pressure waves were investigated. The peak over-pressure inside the second duct decreases for the distance and cross-sectional area ratio between two tunnels to increase. The peak over-pressure and maximum pressure gradient of the pressure wavefront inside the second duct increase as the maximum pressure gradient of initial compression wave increases. The present results were qualitatively well agreed with the results of the previous shock tube experiment.

Attenuation and Distortion of a Compression Wave Propagating in a High-Speed Railway Tunnel.

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel. The attenuation and distortion of the compression wave were measured in three Shinkansen tunnels and the results were compared with the numerical values calculated using a second-order TVD scheme. The strength of a compression wave is exponentically attenuated with distance as it propagates along the tunnel in both slab and ballast track tunnels, and the attenuation in the ballast track tunnel is considerably larger than that in the slab track tunnel. In the slab track tunnel, the compression wave is steepened as it propagates, while it spreads in the ballast track tunnel. The criterion for judgment whether the compression wave is steepend or spreads is expressed by the value of acoustic Reynolds number of about 10∼15.

Theoretical study on compression wave propagating in a sudden reduction duct

Compression waves propagating in a high speed railway tunnel impose large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations can cause ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, a steady theory of Chester-Chisnell- Whitham was applied to a simple shock tube with a sudden cross-sectional area reduction to model trains inside the tunnel. The results of the present theoretical analysis were compared with the experiments of the shock tube. The results show that the reflected compression wave from the model becomes stronger as the strength of incident compression wave and the blockage ratio increase. However, the compression wave passing through the model is not strongly dependent on the blockage ratio. The theoretical results are in good agreement with the experiments.

Numerical study on the interaction between unsteady compression and unsteady expansion wave

A new control method to alleviate the impulsive noise at the exit of high-speed railway tunnel was applied to the compression wave at the entrance of the tunnel. This method uses the interaction phenomenon of unsteady expansion wave and unsteady compression wave. Unsteady expansion wave was assumed to be made instantaneously by the simple theory of shock tube. Total Variation Diminishing method was employed to solve the axisymmetric unsteady compressible flow field with a specified compression wave. Numerical results show that the maximum pressure gradient of the propagating compression wave decreases with increase of the wave length of the unsteady expansion wave. It is found that the impulsive noise reduction can be obtained when the unsteady expansion wave with a large wave length is emitted just before the train enters the tunnel. The present results give the possibility to reduce the impulsive noise at the exit of tunnel.

Experimental study on compression wave propagating in a sudden reduction duct

Compression waves propagating in a high-speed railway tunnel develops large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations would cause an ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, experiments were carried out by using a shock tube with an open end. A blockage to model trains inside the tunnel was installed on the lower wall of shock tube, thus forming a sudden cross-sectional area reduction. The compression waves were obtained by the fast opening gate valve instead of a conventional diaphragm of shock tube and measured by the flush mounted pressure transducers with a high sensitivity. The experimental results were compared with the previous theoretical analyses. The results show that the ratio of the reflected to the incident compression wave at the sudden cross-sectional area reduction increases but the ratio of the passing to the incident compression wave decreases, as the incident compression wave becomes stronger. This experimental results are in good agreements with the previous theoretical ones. The maximum pressure gradient of the compression wave abruptly increases but the width of the wave front does not vary, as it passes over the sudden cross-sectional area reduction.

Numerical study on attenuation and distortion of compression wave propagation into a straight tube

A compression wave is attenuated or distorted as it propagates in a tube. The present study investigated the propagation characteristics of the compression waves which are generated by a train in a high-speed railway tunnel. A Total Variation Diminishing (TVD) difference scheme was applied to one-dimensional, unsteady viscous compressible flow. The numerical calculation involved the effects of wall friction, heat transfer and energy loss due to the friction heat in the boundary layer behind the propagating compression wave, and compared with the measurement results of a shock tube and a real tunnel. The present results show that attenuation of the compression wave in turbulent boundary layer is stronger than in laminar boundary layer, but nonlinear effect of the compression wave is greater in the laminar boundary layer. The energy loss due to the frictional heat had not influence on attenuation and distortion of the propagating compression waves.

Experimental study on reduction of impulsive noise generating at exit of high-speed railway tunnel

As a compression wave is emitted from a duct, an impulsive wave generates and causes an impulsive noise that is at present a serious environmental noise pollution. In order to clarify the acoustic characteristics of the noise and to reduce their pressure levels, a series of model experiments were conducted on the impulsive waves emitted from an open end of a shock tube. The impulsive waves with various intensities were obtained by controlling the operation pressure ratio of the shock tube. Various kinds of silencers such as the exit boxes with baffle plates, were applied to the duct exit to reduce the impulsive noises. The effects of geometry of silencers and shock Mach number on the noise reduction were clarified. From the measurements of sound pressure level, it was found that installing the baffle plate into the exit box is effective in lowering the noise level at far fields, and that the recommendable geometries of silencer are L/D=1, H/D=1 and H/D=0.75.

Grauholz high-speed railway tunnel in difficult ground : Steiner, W Proc International Congress on Tunnels and Water, Madrid, 15–18 June 1988V1, P333–339. Publ Rotterdam: A A Balkema, 1988

Grauholz high-speed railway tunnel in difficult ground : Steiner, W Proc International Congress on Tunnels and Water, Madrid, 15–18 June 1988V1, P333–339. Publ Rotterdam: A A Balkema, 1988

Numerical Study Of Attenuation And Distortion OfA Compression Wave Propagating In A High-speedRailway Tunnel

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel. The attenuation and distortion of the compression wave in the propagation process from the entrance to the exit of the tunnel are studied numerically by a second-order symmetric TVD scheme, taking both fluid friction and heat transfer through the wall into consideration. Numerical results for several examples are given and compared with the results measured in real high-speed railway tunnels of the Shinkansen line in Japan.