Investigating the Influence of Pitch Rate and Pivot Location on Aerodynamic Performance and Leading-Edge Vortex Dynamics of Rotating and Pitching Flat Plates

Unsteady flow separation and leading-edge vortices (LEV) greatly affect the aerodynamic performance of insect wings, helicopter rotor blades, among others. Such unsteady aerodynamic phenomenon is strongly influenced by pitch rate and pivot location of the wing. The present investigation employs direct force measurement and particle image velocimetry to study a rotating and pitching flat plate. An aspect ratio 6 flat plate, rotating at a tip velocity-based Reynolds number of 5000 and pitching from 0-90^o is used. The effects of varying reduced pitch rate K and pitch pivot locations x_p/c on the aerodynamic lift C_L and drag C_D coefficients, as well as the LEV system is investigated. The results show a generalization in scaling of C_L and C_D with K and x_p/c and relate such scaling to the formation and growth of LEVs. Higher K results in peak values of C_L and C_D coefficients occurring at higher pitch angles but have higher peak values than at lower K. On the other hand, moving x_p/c from leading edge towards the trailing edge delays separation but this results in decreasing LEV strength and subsequently lower C_L and C_D peak values. Furthermore, for different x_p/c, a convective time shift is successful for collapse of C_L and C_D peaks at same non-dimensional convective time t^*.