Laminar Vortex Shedding in the Wake of a Cube

Abstract

Flow around a cube is numerically studied in the laminar vortex shedding regime. The objective is to examine the three-dimensional vortex shedding mechanism and understand the temporal behavior of the wake. Vortices were identified using λ2 criterion for Re = 250–770. The wake of the cube sheds paired hairpin vortices, which moves in the streamwise direction and attains a constant shape with time. The analysis of separation distance and angular orientation of hairpin vortices for flow around a cube are presented here for the first time in the literature. The separation (d) between the paired hairpin vortices scales as t−1/2. The orientation of hairpin vortices changes with time and attains a near-normal orientation with respect to the axial direction. At Re ≥ 339, the hairpin twists with respect to axial direction losing the axisymmetry in one plane noted for 276 ≤ Re ≤ 300. The hairpin vortices disintegrate into smaller vortices at higher Re = 570 and 770. A quasi-periodic nature of the flow has been revealed by the phase plots. The drag and side forces generated due to the flow are studied with pressure force mostly contributing to the drag. One of the side force coefficients dominates owing to the asymmetry of the wake in one plane and symmetry in the other orthogonal streamwise plane. These results clearly bring out the asymmetric nature of flow in the shedding regime.