Influence of relative thickness on static and dynamic stall characteristics and prediction of airfoils

A study was conducted to investigate the effects of relative thickness on the static and dynamic characteristics of airfoils. A series of NACA symmetric airfoils with relative thickness ratios ranging from 12% to 30% have undertaken a series of sinusoid pitching motion simulations and these airfoils' Glasgow wind tunnel experiment data were analyzed. It was found that the relative thickness of airfoils would affect the stall onset angle of attack (AOA), the severity of the stall, and the dynamic stall model parameters. As the relative thickness of airfoils increases, static and dynamic stall onset AOA decrease and stall occurs earlier. At the static AOA, the thickest airfoil shows a very large reverse flow region. At the dynamic stall onset AOA, the thinner airfoil exhibits a more obvious burst of the laminar separation bubble. When the relative thickness of the airfoil is smaller, a dynamic stall occurs with more severity. On the one hand, the aerodynamic characteristic curve and suction surface pressure curve of airfoils change are more complicated. And the severity of the dynamic stall was quantitatively compared by extracting the difference of lift coefficients corresponding to the same AOA in the upstroke and downstroke stages. On the other hand, vortex occurrence, convection and shedding on the suction surface of the airfoil are more frequent and complicated. This paper also gives a method to solve the problem of the lack of the dynamic stall model parameters of blades section airfoils when predicting the wind turbine's unsteady force.