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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.

It is necessary to obtain the aerodynamic force coefficients of the train on the embankment for the assessment of the running safety in a crosswind. In general, wind tunnel tests are conducted using the static train model on the embankment model. In this paper, the influence of the airflow condition and the distance from the upstream end of the embankment model to the train model on the aerodynamic force coefficients is investigated. In the wind tunnel tests, the side force coefficients (CS) reached their maximum values at a yaw angle of 50° in smooth flow while they reached their maximum values at a yaw angle of 90° in atmospheric boundary layer (ABL) flow. Large-eddy simulation (LES) was made on the flow around the train model on the embankment, and it was found that CS became larger as the upstream embankment length became smaller owing to the vortex generated near the upstream end of the embankment at the yaw angle of 50°. LES on the flow around the embankment model showed that the distance over which the flow field was affected by this vortex was 16 times the height of the embankment model in smooth flow, and it was 12 times in ABL flow at the yaw angle of 50°.