Effect of Aspect Ratio on Swept-Wing Dynamic Stall

Abstract

The role of aspect ratio on the dynamic stall process of swept finite wings is investigated using high-fidelity implicit large-eddy simulations. Two aspect ratios ([Formula: see text] and 8) are explored for a 30 deg swept wing (NACA 0012) pitching sinusoidally from an initial incidence of 4 deg to a maximum angle of attack of 22 deg with a reduced frequency of [Formula: see text] over one pitching cycle. The flow is simulated at a chord Reynolds number of [Formula: see text] and a freestream Mach number of [Formula: see text]. The unsteady three-dimensional flowfield for the higher-aspect-ratio wing showed similarity with the lower-aspect-ratio wing through the initial flow separation at the leading edge. Motion-induced effects promoted earlier initiation of the unsteady vortical structures at higher aspect ratios. The vortex tube at the larger span underwent significant distortion, which contrasted with the [Formula: see text] vortex observed at the lower span. The vortical structure eventually interacted with the trailing-edge vortex, which was not observed at [Formula: see text]. Examination of the unsteady loads detailed a larger lift slope, mean values, peak values, and earlier stall as the aspect ratio increased. Analysis of the aerodynamic pitch damping suggests the [Formula: see text] wing is less susceptible to local torsional instabilities than the [Formula: see text] wing.