Transitional Separated Flow Over Low-Aspect-Ratio NACA0012 Wings

Three-dimensional transitional separated flow over low-aspect-ratio NACA0012 wings (semi-aspect ratios of sAR = 1 and 2) is numerically investigated at Reynolds numbers of 1× 10⁴ and 4 × 10⁴, across a range of angles of attack from 10° to 20°. The numerical simulations are performed by solving the unsteady Reynolds-averaged Navier-Stokes (URANS) equations, employing the transitional turbulence model of shear stress transport (SST) γ − Re_θ to simulate the turbulent flow and predict the laminar-to-turbulent transition. It is observed that the lower aspect ratio wing (sAR = 1) produces lower lift and drag coefficients than the higher aspect ratio wing (sAR = 2), regardless of the Reynolds number. For sAR = 1, the lift coefficient increases monotonically with angle of attack, whereas sAR = 2 exhibits the opposite trend at Re = 1 × 10⁴. At lower aspect ratios, the downwash induced by the wingtip vortices affects a broader spanwise region. The spike in the sectional lift coefficient is found closer to the root for sAR = 1. Moreover, the separation and transition points are observed earlier for the higher aspect ratio wing. For sAR=1, the wake remains steady under all tested conditions due to the strong downwash effect. This steady wake behavior may be influenced by the turbulence modeling, which can suppress low-frequency vortex shedding compared to LES or DNS simulations. In contrast, the unsteady flow and Karman vortex shedding appear across the midspan when the downwash weakens for sAR=2.