Relations between shear flow and vortices in the near wake of a high speed train

Abstract

Two flow cases for high speed train models with different lengths have been numerically computed by performing the improved delayed detached-eddy simulation. Based on the Omega method and turbulence production (TP) distribution, the relations between the shear flow and vortices in the near turbulent wake of a high speed train have been comparatively analyzed. First, in the wake region immediately close to the tail, the boundary layer separation plays significant roles. And the mechanism makes shear deformation prominent in the region with the formed vortices. Moreover, the shear layers are pertinent to the boundary-layer thicknesses and help to the TP distribution. However, the shear-dominated region is very limited due to high dissipation. One the other hand, a vast majority of the vortices captured with the parameter Omega increasing in the downstream region away from the tail. And the TP distributions are stable at different streamwise positions, though obviously decreased. They are greatly attributed to the mean strain rate in the horizontal plane. Meanwhile, the vortical vorticity is thought to be the dominant component inside the vortex cores, although the shear becomes weaker. And thus the turbulence itself can be spatially sustained due to the relatively stable vortex structure. Moreover, the weak shear is believed to depend upon the interaction between the vortices and the ground.