Transitional Separated Flow Over Low-Aspect-Ratio NACA0012 Wings

Three-dimensional transitional separated flow over low-aspect-ratio NACA0012 wings (semi-aspect ratios ofsAR= 1 and 2) is numerically investigated at Reynolds numbers of 1 × 104and 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 −Reθto 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), independent of the Reynolds number. ForsAR= 1, the lift coefficient increases monotonically with angle of attack, whereassAR= 2 exhibits the opposite trend atRe= 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 forsAR= 1. Moreover, the separation and transition points are observed earlier for the higher aspect ratio wing. ForsAR= 1, the wake remains steady under all tested conditions due to the strong downwash effect. This steady wake behaviour may be influenced by the turbulence modeling, which can suppress low-frequency vortex shedding compared to LES or DNS simulations. Whereas the unsteady flow and Karman vortex shedding appear across the midspan when the downwash weakens forsAR= 2.