Shearless and sheared flow past a circular cylinder: Comparative analysis by means of LES

Large eddy simulation (LES) of the uniform shear flow past a circular cylinder at Reynolds number Re_D = 3900 with increasingly enhanced mean shear magnitude {divides}du_F/dy{divides} corresponding to the shear rate (SR = {divides}du_F/dy{divides}D/u_F) range between 0 (shearless flow) and 0.177 have been performed in order to provide a basis for comparative analysis of the shear-induced effects with respect to the structural characterization of the cylinder wake. The case characterized by the velocity gradient being perpendicular to the cylinder axis was considered. In addition to the direct comparison of the present computational results with the reference database (mean velocity and Reynolds stress profiles at selected locations in the near and the far wake), the results presentation includes pressure field around the cylinder, mean pathlines inside and outside the separation bubble, vortex structure visualization by the pressure fluctuations and Q-criterion as well as the Reynolds stress anisotropy evolution and energy budgets of the Reynolds stress components and the kinetic energy of turbulence. An important outcome arising from the present computational study relates to the asymmetric shape of the mean quantity profiles with the local maxima/minima shifted to the high velocity side, indicating a strong modulation of the large-scale structures in the wake due to the imposed mean shear. It applies especially to the far wake region. Here, the structures illustrated by the fluctuating pressure field clearly show their existence only on the high velocity side. In contrast, the small-scale structures remain almost unaffected by the mean shear. Evaluation of the lift forces from the velocity and pressure fields illustrate an increasing magnitude with the shear rate towards the lower velocity side, in good agreement with corresponding experiments.