Flow mechanism for the effect of pivot point on the aerodynamic characteristics of a pitching airfoil and its manipulation

Abstract

The effects of pivot point location on the aerodynamic characteristics of a pitching airfoil were numerically investigated. The aerodynamic loads and evolution of flow structures for the fixed-pivot pitching airfoils with different pivot locations were studied first. It was found that the leading-edge vortex grows earlier and the lift coefficient becomes larger with the forward movement of the pivot location during the upstroke motion, which shows an opposite variation during the downstroke motion. Such trend stems from the phase lag in flow evolution of different cases. Thus, a new definition of the effective angle of attack for pitching motions was proposed, and it was found that this parameter could well unify the variations of lift coefficient and vortical evolution caused by the pivot location. The data assimilation indicates that the effective angle of attack is the dominant factor of pivot effect for most time of a period, which reveals the flow mechanism of the pivot effect. This definition was further extrapolated so that it could also be applied to the pitching-plunging motions. Furthermore, a movable pivot pitching scheme by combining respective advantages of fixed-pivot pitching airfoils with different pivot locations was proposed, and it was indicated that the lift performance of the dynamic airfoil could be improved.