On uniform planar shear flow around a circular cylinder at subcritical Reynolds number

Abstract

An experimental investigation was conducted of a circular cylinder immersed in a uniform planar shear flow, where the approach velocity varies across the diameter of the cylinder. The study was motivated by some apparent discrepancies between numerical and experimental studies of the flow, and the general lack of experimental data, particularly in the subcritical Reynolds number regime. Of interest was the effect of shear on the vortex-shedding frequency and the mean aerodynamic forces, including the direction and origin of the steady mean lift force experienced by the cylinder, which has been the subject of contradictory results in the literature and for which measurements have rarely been reported. The circular cylinder was tested at Reynolds numbers from Re=4.0×10 4 to 9.0×10 4, and the dimensionless shear parameter ranged from K=0.02 to 0.07, which corresponds to a flow with low to moderate shear. The results from both the present and previous studies show that low to moderate shear causes a small increase in the Strouhal number, an increase in the mean base pressure coefficient, a reduction in the mean drag force coefficient, and a small mean lift force directed towards the low-velocity side. These effects are consistent with a narrowing, or reduction in width, of the cylinder near wake, which is supported by an asymmetric mean static pressure distribution on the surface of the cylinder.