Aerodynamic characteristics during the side reattachment evolution process of 2:1 rectangular cylinder under different Reynolds numbers

Three-dimensional (3D) large-eddy simulations of a 2:1 rectangular cylinder were conducted within the Reynolds number (Re) range from 500 to 22 000 using standard Smagorinsky model. The study focuses on the evolution of the flow field and the variation of the aerodynamic forces during the side reattachment process with the Reynolds number. Time-averaged analysis indicates that the occurrence of reattachment is intermittent. As the Reynolds number increases, the phenomenon of the side reattachment decreases, accompanied by a decrease in time-averaged pressure and the fluctuating pressure. The main flow field of controlling the pressure has undergone a transition from the reattachment phenomenon (low Re) to secondary vortices (medium Re) to side recirculation bubble (high Re). The instantaneous analysis shows that reattachment is the cause of the double-peak waveform in the time histories of lift coefficients. At the moment when reattachment occurs, the streamwise shear stress and the pressure reach the maximum value. The reduction in reattachment phenomenon leads to a decrease in the peak instantaneous pressure and a rearward shift in its occurrence. The reduction of the reattachment decreases the peak pressure and shifts its occurrence location downstream. Streamwise shear stress drops as spanwise shear stress rises, indicating stronger three-dimensional (3D) characteristic. This work clarifies the development mechanism of reattachment unstable flow and its correlation with aerodynamic force. This facilitates the understanding of the effects of reattachment phenomenon on structural responses during vibration.