Numerical and experimental study on flow separation control of airfoils with various leading-edge tubercles

In recent years, leading-edge tubercles of humpback whales have received increasing attention as a passive stall control mechanism. The control mechanism and flow field structure of a reference (ref) and two modified airfoils (mod-1 and mod-2) are investigated numerically and experimentally at a Reynolds number of Re = 5 x 105 in this paper. The results demonstrate that the lift coefficient of the modified airfoils is enhanced to a certain extent after these airfoils stall. In addition, the stall processes of mod-2 are smooth and stable over the observed sudden decrease in ref. Counter-rotation vortex pairs (CRVPs), which improves momentum exchange in the trailing edge boundary layer on the suction side, according to streamline slices and iso-surfaces of the vorticity. Moreover, interaction between streamwise vortices is the main reason for the improved hydrodynamic characteristics at high angles of attack (AOAs). Furthermore, when smoke visualization is carried out in a low-Re wind tunnel, mod-1 and mod-2 exhibit similar characteristics, vortex pairs are periodic and symmetric along the wingspan direction at alpha = 5 degrees, and vortex pairs begin to interact and influence flow separation at alpha = 15 degrees. Finally, numerical analysis of the characteristics of tubercle turbines is conducted. The findings reveal that the energy efficiency can be enhanced within a narrow range of tip speed ratios (TSRs).