Experimental investigation on the aerodynamics and flow patterns of a 5:1 rectangular cylinder with spoilers

The current study experimentally investigates a passive control method for the flow field by placing spoilers symmetrically on the leading edge of a 5:1 rectangular cylinder. The Reynolds number (Re) is based on the inflow velocity and the height of the model. The length of the spoiler is equal to the span length of the model, and the width and angle are defined as w and α. At $\text{Re = 1.07 2.50}\times {\text{10}}^{\text{4}}$, the surface pressure distribution of the model is obtained to initially investigate the effects of α and w on the aerodynamic characteristics. Based on the aerodynamic results, some cases are selected to reveal the control mechanism using the particle image velocimetry (PIV) technique. The proper orthogonal decomposition (POD) is adopted to analyze the POD modes and instantaneous flow. The results show that the spoiler with a certain α can suppress the aerodynamic forces of the model. Spoilers with a relative angle of 247.5° significantly reduce ${\text{C}}_{\text{L}}^{\prime }$ by 75 % and slightly reduce $\overline{{\text{C}}_{\text{D}}}$ by 5.5 %. Also, its TKE and RSS values are reduced by 56 % and 57 %, respectively. The PIV visualization shows that the spoiler affects the flow separation at the leading edge. Then, the rolling and interactions of shear layers are suppressed, making them tend to be parallel. Besides, spoilers with a relative angle of 67.5° almost eliminate the flow separation.