Reducing slipstream velocities around high-speed trains through retractable stationary surfaces

Abstract

The slipstream wake structures generated by the passing of high-speed rail vehicles represents a hazard to passengers and workers in close proximity, and as such, maximum allowable slipstream velocities are prescribed in regulations. In this article, the possibility of reducing peak slipstream velocities using retractable or foldable local surface modifications on a generic high-speed train is assessed using Improved Delayed Detached Eddy Simulation (IDDES) modelling. It is demonstrated that the danger imposed by the slipstream wake structures, as measured by the induced velocities recorded at a pair of parallel test lines, as dictated in the standards, could be reduced by designs employing each of three methods examined. The most dramatic reductions were generated by large fins at the train rear, which redirected the time-mean trailing vortex structures to one side of the vehicle. However, the most feasible control method for symmetrical slipstream reduction consisted of placing small rectangular plates perpendicular to the flow near the nose section of the train. The induced disruption to the flow was observed to increase wake turbulence in a region above the train, which appeared to interfere with the formation of the trailing vortex structures and reduce the intensity of the cross-stream oscillation.