Evolution of Vortex Formation in the Wake of Thin Flat Plates with Different Aspect-Ratios

Abstract

The effect of aspect-ratio (AR) on the formation and interaction of vortical structures in the wake of normal thin flat plates is examined at Re $=$ 1200 using an infinite span (2D) plate and rectangular plates (${ AR}=1.0$, 1.6 and 3.2). The vortex shedding frequency significantly increased for ${ AR}=3.2$ compared to the 2D plate, while it dropped for ${ AR}=1.6$ and 1.0. The lowest frequency of vortex shedding was observed for ${ AR}=1.0$. Shear layers rolled to form vortices closer to the plate leeward surface at higher AR. The mean recirculation length was longer for the 2D plate compared to rectangular and square plates. The interaction of shear layers originating at the edges of the rectangular plates led to the formation of vortex loops in the wake. The wake appeared less organized for the lower AR plate (1.6) with a higher turbulence energy compared to ${ AR}=3.2$. The magnitude of turbulence kinetic energy was lowest at ${ AR}=3.2$ and it increased with decreasing AR. The mean drag coefficient was $\approx$2 for the 2D plate and $\approx$1 for ${ AR}=1$, which suggested major differences in the wake structures.