The Effect of Aspect Ratio on Torus Wake Structure

Abstract

AbstractThe present investigation deals with the flow behind a torus, placed normal to the flow direction in three different aspect ratios (defined as the main diameter to the cross-sectional diameter of the torus) of 2, 3 and 5 at a constant Reynolds number of 9000. The Large Eddy Simulations (LES) are carried out to model the three-dimensional flow field around the torus. Wake structure, turbulence properties and force characteristics are investigated. Three shedding frequencies are detected at the Reynolds number studied. The highest frequency is attributed to the small-scale instability of the separating shear layer, the second one is a vortex shedding frequency that increases with aspect ratio, and the lowest one is due to the pulsation of the inner shear layer that can be observable for aspect ratios of 2 and 3. The torus has a blockage effect on the flow which is dependent on the center hole size. For the higher aspect ratio, the flow structure develops quickly, the wake flow is influenced by both inner and outer shear layers, thus forming the regular vortex ring patterns. For the lower aspect ratios, the flow pattern is mainly governed by the interaction of the outer shear layers. The results align well with documented experiments in the literature.KeywordsTorusWake structureVortex sheddingLESTurbulence