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Predicting the aerodynamic phenomena in a train-tunnel system is important for increasing the speed of railway trains. Among these phenomena, many studies have focused on the effects of pressure; however, only a few studies have examined the effects of flow velocity. When designing train roof equipment such as a pantograph and an aerodynamic braking unit, it is necessary to estimate the flow velocity while considering the influence of the boundary layer developed on the train roof. Until now, numerical simulations using a one-dimensional model have been utilized to predict the flow velocity around a train traveling through a tunnel; however, the influence of the boundary layer cannot be taken into consideration in these simulations. For this purpose, the authors have previously proposed a simple calculation method based on a steady incompressible tunnel flow model that can take into account the influence of the boundary layer, but this method could not incorporate the unsteadiness of the flow velocity. Therefore, in this study, the authors extend the previous simple calculation method such that it can be used for an unsteady incompressible tunnel flow. The authors compare the calculation results obtained from the extended method with the results of a model experiment and a field test to confirm its effectiveness.

A pantograph mounted on a high-speed train roof is exposed to high-speed air flow while traveling, and lift force is generated in the pantograph. To ensure high current collecting performance of the pantograph, it is important to appropriately adjust the lift force generated in the pantograph. The flow velocity along the roof of a train has a significant influence on the lift force. In this study, we proposed a simple calculation method that enabled us to easily calculate the flow on the train roof in a tunnel using a personal computer. To validate the effectiveness of the proposed method, model experiments were carried out and calculation and experimental results were compared. Furthermore, the influence of hydraulic friction coefficients on train roof flow velocity was examined using the proposed method, which was not time consuming.

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.

Compression waves generated by a high-speed train entering a tunnel were measured in three Shinkansen tunnels and the results were compared with the numerical values calculated using the TVD scheme. The strength of a compression wave is exponentially 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 steepened or spreads is expressed by the value of acoustic Reynolds number of about l0∼15.

When high-speed trains are running and passing each other in a tunnel, these generate compression waves ahead of trains. These waves are propagated through the tunnel and causes a large pressure transients are generated against trains. It is necessary to predict these pressure transients accurately in planning speed-up of Shinkansen trains. From this point of view, it is important to clarify the formation mechanism of pressure transients and the waveform of the pressure wave generated by the trains passing each other in a tunnel. In this paper, pressure transients are calculated by characteristic method in the high-speed train/tunnel systems and the formation mechanism of pressure transients is clarified.

A high-speed train entering a tunnel generates a compression wave ahead of it. The wave is propagated through the tunnel and causes an impulsive noise when it arrives at the tunnel exit. The magnitude of impulsive noise from the tunnel exit is proportional to the maximum time rate of pressure change of the compression wave reaching the exit, according to the aeroacoustic theory. From this point of view, it is important to clarify the formation mechanism and the waveform of the compression wave generated at the entrance of the tunnel. In this paper, the entry compression waves are measured in actual high-speed train/tunnel systems and the results are compared with the theoretical values. Then the formation mechanism of the entry compression waves is clarified.

The unsteady boundary layer induced by propagating compression wave has been investigated by means of a recently developed laser differential interferometry (LDI) method using Wollaston prisms. The difference of the two detector signals in LDI will therefore be essentially free of vibrations and laser output variations. LDI can be made more sensitive to optical path changes by 2 to 3 orders of magnitude than in classical interferometry. The sensitivity was sufficiently high to record the density variations by compression waves. The measurements of the time-dependent profiles gave detailed information on the process of formation of the unsteady boundary layer induced by propagating compression wave in a constant-area duct. It was found that the laminar-to-turbulent transition in unsteady boundary layer flow, which describes the density profiles at a strength of the initial compression wave from 9 kPa, exists.