Aerodynamic characteristics of a rounded-corner square cylinder in shear flow at subcritical and supercritical Reynolds numbers

Abstract

Shear-inflow effects on flows past a rounded-corner square cylinder is investigated when Reynolds number (Re) increases from subcritical regimes (Re=2.2×104) to supercritical regimes (Re=1.0×106), with a focus on the latter Re in this study. The dimensionless shear parameter K ranges from 0 to 1.0. Results show that shear inflows have different effects on the aerodynamic characteristics of the cylinder in two Re regimes, and generally shear effects are smaller when Re is in the supercritical region. Specifically, mean and r.m.s pressure distributions remain in the same shapes under all shear inflows tested at supercritical Re; however they witness strong dependency on K at subcritical Re. Moreover, the directions of mean lifts at supercritical Re are opposite to those at subcritical Re. Correspondingly, the mean flow patterns observed in the uniform flow are overall preserved in shear flows at the supercritical Re: the free stream flows along the cross section and separates from the trailing corners on both sides of the cylinder, despite of the existence of small-degree asymmetry in the near-wake. However, the flow patterns are significantly changed at the subcritical Re by the sufficiently high shear inflows: the shear layer in suspension tends to reattach on the side wall of the high-velocity side and eventually separates from the trailing edge while the other on the low-velocity side becomes farther from the side wall. It results in the near-wake forming along an axis rotated in the clockwise direction from the horizontal axis, being opposite to the anticlockwise direction at supercritical Re. The mechanism for Re effects is further explored. The preservation of overall flow pattern at supercritical Re even under the strong shear effects is suggested mainly due to the greater favorable pressure gradient and the induced greater velocity acceleration before flow separation on the low-velocity side.