Effects of Length on Aerodynamics of High Speed Train Models

Abstract

Effects of length on train aerodynamics were investigated using computational fluid dynamics (CFD). The numerical study was used to obtain the aerodynamic forces and the flow field of various length models. A comparison of aerodynamic drags among these models, and investigation of the flow field causing these differences were made. The drag coefficient of head cars basically unchanged. As the turbulence boundary layer thickness grows, the drag coefficient of each middle car along flow direction decreased slightly both in pressure and viscous. The drag coefficient of tail cars decreased about 10% from 2 cars to 4 cars model. The antisymmetry helical vortex occurs close to the ground, and extends a considerable distance into the train wake. The distance of vortex cores remain constant within 0.4l, and get closer after 0.6l behind the tail cars. The results indicate 2 cars model can represent longer train in wind tunnel test and the correction is required