Numerical Simulation of Flow Around a Train

It was recognized that the vibration amplitude of the tail car is greater, especially in the tunnel, than that of the other cars in a high-speed train, in which an aerodynamic force has some effects. However, few aerodynamical studies have been conducted and little knowledge has been gained. To clarify the aerodynamical effect on the train, a three-dimensional unsteady Navier-Stokes simulation was carried out. Unsteady flow separations on the rear nose, which cause fluctuations of the yawing moment of the tail car, were successfully obtained by the simulation. In the tunnel section, it is proved that the tunnel wall makes the flow separation asymmetric and that the expansion of the effective flow area along the rear nose causes a greater pressure fluctuation. We also proposed a modified shape of rear nose, which suppresses the flow separation and reduces the yawing moment fluctuation.