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DIRECT NUMERICAL SIMULATION OF THE WAKE OF A NORMAL THIN FLAT PLATE: INFINITE VS. FINITE WIDTH

Arman Hemmati
Department of Mechanical and Manufacturing Engineering University of Calgary, AB, Canada; Department of Mechanical and Aerospace Engineering, Princeton University, NJ, USA

David H. Wood
Department of Mechanical and Manufacturing Engineering University of Calgary, AB, Canada

Robert J. Martinuzzi
Department of Mechanical and Manufacturing Engineering Schulich School of Engineering, University of Calgary 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4

Abstract

The wake of a normal thin flat plate of aspect ratio 3.2 was studied using Direct Numerical Simulations at a Reynolds number of 1200 for comparison to the wake of a two-dimensional (2D) plate. Secondary spanwise instabilities, which were responsible for the three distinct flow regimes in the wake of 2D plates, were suppressed by the presence of the shear layers formed at the shorter edges in the three-dimensional (3D) case. There was a unique vortex "peeling" mechanism that detached the vortices in the shear layers on the shorter sides. The peeling mechanism accelerated the shedding process and increased the shedding frequency to 0.317 from 0.154 for 2D plates. It is also associated with increased wake entrainment and a reduction in the mean recirculation length by 40% to 1.6h. Moreover, the peeling mechanism lead to formation of interlocked vortex loops outside the base region, whose expansion downstream resulted in separation of two counter-rotating vortex structures with respect to the wake centreline. The maximum turbulent kinetic energy along the wake centreline for the 3D case was lower by 76% than in the 2D flow.