Effect of sinusoidal vertical gust on the pressure distributions on and flow structures around a rectangular cylinder

The effects of turbulence on separated and reattaching flows around rectangular cylinders have been extensively studied. However, less knowledge exists regarding the effects of oscillatory gusts on separated and reattaching flows. In this paper, the surface pressures on and the flow structures around a 5:1 rectangular cylinder under the effects of sinusoidal vertical gusts in separated and reattaching flows are studied through wind tunnel experiments by pressure and particle image velocimetry (PIV) measurements. The results show that the effects of gust amplitudes are more pronounced than those of reduced gust frequencies. As the gust amplitude increases, the maximum of the RMS pressure coefficient (C̃_p) increases and the size of the separation bubble reduces remarkably. Additionally, the dominant spanwise correlated regions on the upper and lower surfaces of the cylinder become broader at different attack angles. The analysis of the pressure measurements demonstrates that the pressure fluctuations are mainly generated from the periodic oscillations of gust velocities, which makes the maximum of C̃_p insensitive to the change of attack angle. Meanwhile, the interactions between the pressure fields excited by gusts and separated and reattaching flows may result in relatively smaller maximums of C̃_p on the upper surface in the sinusoidal vertical gusts compared with those on the lower surface at large attack angles. The PIV measurement results show that the turbulent kinetic energy increases under the effects of sinusoidal vertical gust. In addition, the impingement of shear layers and the vortex swirling strength become more intense with the increased gust amplitude.