Identification method of vortex structures around vehicle

Abstract

In order to identify vortex center axes around the vehicle from the result of computational fluid dynamics, a method focusing on the pressure minimum is proposed. The sectional-pressure-minimum-and-swirl method can identify vortices that are low pressure at center points and swirling in homogeneous isotropic turbulence. In this paper, it is extended to be applicable to the flow field around vehicles with unstructured grids in three steps. First, spherical projection method is used to determine whether the vortex center point is inside or outside an unstructured grid of various shapes. Second, a vortex center axis grows in two directions, the front and the back a plane perpendicular to the vortex axis and imposes two angle conditions to prevent fragmentation. Finally, the vortex center axes are filtered by the number of vortex center points. In order to verify the effectiveness of the proposed method, some vortex identification methods were used for the flow field around the sedan. The flow filed was a time-averaged flow field calculated by large eddy simulation. As a result of comparing to the previous method, the proposed method prevented fragmentation of vortex center axes. The proposed method could identify four known vortex structures obtained by the isosurface method. Compared to another commonly used methods, the proposed method did not connect the vortices and briefly visualized the vortex center axes.