Experimental investigation of aerodynamic performance of oscillating wings at low Re numbers

Abstract

In this study, the effect of varying aspect ratios on aerodynamic performances on the flat plate and NACA 2415 airfoil without/with low frequency pitching movement at low Reynolds (Re) numbers was investigated. The experiments include force measurements for both static and dynamic airfoils and smoke-wire flow visualization for static airfoils at Re numbers of 50,000, 75,000 and 100,000. In the static cases, the stall delayed because of tip vortices at low aspect ratios, as the aspect ratio increased, maximum lift coefficient and the stall angle decreased. On the other hand, the stall mechanism changed and the abrupt stall occurred. As the Re number increased, the mild stall formed. In the dynamic cases, on the flat plates at lower ARs, the oscillation did not change the lift coefficients considerably, and as the Re number increased, the oscillation made the drag force decrease. In the dynamic NACA 2415 wing with AR1, the oscillation improved the aerodynamic performance at down-stroke conditions (especially between 15° and 25°). However, in dynamic NACA 2415 wing with AR2, as the Re number increased, dynamic stall formed over the wings at the angle of attacks between 15° and 25°.