Characterizing three-dimensional features of vortex surfaces in the flow past a finite plate

We extend the vortex-surface field (VSF), a Lagrangian-based structure identification method, to investigate vortex dynamics in flows past a plate simulated by the immersed boundary method. As an example, the VSF evolution characterizes the three-dimensional features of vortex surfaces in the flow past a finite plate at the Reynolds number of 300, aspect ratio of 2, and angle of attack of 30°. The VSF isosurface displays that near-plate vortex surfaces first roll up from plate edges and then evolve into hairpinlike structures near the leading edge and semiring structures near plate tips and in the wake. We quantitatively distinguish two types of vortical structures by the vanishing streamwise vorticity on VSF isosurfaces and refer them to as the leading edge vortex (LEV) and the tip vortex (TIV). Based on circulations through cross sections of vortex surfaces, we demonstrate that the lift generated from the LEV is suppressed by the finite growth of TIVs. In the wake region, we quantify the geometry of helical vortex lines in TIVs and the contribution of the helical vorticity component to the streamwise vortical impulse.