Vortex control strategy for unsteady aerodynamic optimization of a plunging airfoil at a low Reynolds number

Abstract

This study has explored effective flow control strategies to improve unsteady aerodynamic performance of a plunging airfoil at a low Reynolds number of Re = 59 000 through controlling the leading-edge vortex (LEV) formation and development. The leading-edge blowing control is first utilized to directly strengthen the LEV by injecting momentum into the separated leading-edge shear layer. The influence of the momentum coefficient on the vortical evolution and aerodynamic forces is more significant than that of the exit width. As the momentum coefficient increases in a certain range, the LEV can be enhanced, thereby increasing the maximum unsteady lift. However, it is found that an accelerated detachment usually occurs with enhancement of the LEV as the secondary vortex is also promoted by blowing, leading to a reduced duration of high lift compared with the baseline case. In order to solve such a control problem of the LEV, the control strategy of the combined blowing and suction is further proposed, which could increase the LEV strength and concurrently delay the LEV detachment to some extent through inhibiting the growth of the secondary vortex. As a result, the unsteady aerodynamic performance of the plunging airfoil has been further improved with a significant increase in the maximum lift coefficient and a moderately prolonged duration of high lift.