An Experimental Study of Unsteady Flow Structures in the Wake of a Train Model

Abstract

Trackside induced airflow velocities are an important criterion for the design of trains. The maximum velocities are typically observed in the train wake and are caused by larger turbulent flow structures. The wake flow depends not only on the geometry of the train’s tail but also on the boundary layer. Due to the limited model size and different Reynolds numbers in model experiments, the wake flow may not be comparable to real trains. The idea is to control the thickness of the boundary layer using roughness elements independently from the model speed and lengths. High-speed particle image velocimetry is used to measure the flow velocities in a plane parallel to the ground at two different heights. As expected, the measured velocities vary greatly between the individual runs. Conditional sampling is used to analyze the size and dynamics of the flow fields at the time of maximum velocity. The results show, that the roughness elements in this setup affect the boundary layer and the flow structure at the lower height by increasing the average and maximum velocity. It remains to investigate, if an applicable setup of roughness elements can be found to create a realistic wake flow compared to real trains.