A large eddy simulation is conducted over a real-shaped four-car train model to investigate the relationship between meandering flow generated beneath the underbodies and unsteady slipstream velocity in the wake of the train. A wind tunnel test, which measures slipstream velocity in the wake, is conducted to verify the validity of the computational result in the stationary ground condition. Similar peaks in slipstream velocity are observed in the wake of the train in both the experiment and computation, thereby demonstrating the validity of the computational result. Slipstream velocity indicates the magnitude of the flow velocity in the ground coordinate system, and therefore becomes larger behind the tail of the train, where the flow is sucked in. On the other hand, a large-scale meandering flow structure develops beneath the underbodies, exerting a significant influence on the wake. In order to investigate the relationship between the unsteady slipstream characteristic and the periodic meandering flow, the phase-averaging method is applied to the flow field. It is found that the maximum velocity of the slipstream along the streamwise line, at a distance equal to the car width from the center of the car near the ground, increased in synchrony with the meandering flow. This finding suggests that the slipstream velocity distribution fluctuates unsteadily due to the meandering flow.
ABE et al. (Wed,) studied this question.