Flow around a 5:1 rectangular cylinder: Effects of upstream-edge rounding

A sensitivity analysis of highly-resolved large-eddy simulations of the flow around a 5:1 rectangular cylinder to the introduction of a small rounding of the upstream edges is presented. Different values of the edge radius of curvature are considered, in a range such that they might reasonably be ascribed to manufacturing tolerances. A stochastic approach is adopted in order to build response curves of the quantities of interest as a function of the radius of curvature. The considered computational set-up, characterized by a fine numerical resolution and a low subgrid-scale (SGS) dissipation, predicts for the body having perfectly sharp edges a short mean recirculation length on the cylinder side, in disagreement with experimental data. On the other hand, even for the smallest considered radius of curvature, the length of the mean recirculation region increases significantly and, hence, the agreement with the experimental data is much improved. It is observed that the sharp edge introduces a higher level of turbulent fluctuations in the shear-layer at separation, which, if not artificially damped by numerical or SGS dissipation, grows faster and leads to a further upstream roll-up of the shear-layers and, hence, to a shorter mean recirculation region than in simulations with rounded edges.