Fluctuation levels in the wake of a shedding cylinder in shear flow

Abstract

The effects of the presence of a boundary layer type of upstream shear profile on the characteristics of vortex shedding from a cylinder of L/D = 24 were experimentally investigated in a low-speed wind tunnel using hot-film anemometry. The shear (steepness) parameter β was 0.016 and the Reynolds number was 5 × 104. The results show that although the effect of shear on the rms value of the velocity fluctuations in the wake was minor, its effect on the frequency content of the velocity signal was substantial. It was also found that shedding was strong and vortices were well correlated along the cylinder in the case of uniform upstream low-turbulence flow. On the other hand, high-turbulence upstream shear flow caused vortices to be shed in uncorrelated cells and caused the shedding process to be substantially weaker and unstable compared to the case with no shear.