Boundary-Layer Flow Effects on Aerodynamic Performance of Forward-Swept Wings

The effects of a forward-sweep angle (phi), Reynolds number (R), and angle of attack (alpha) on the boundary-layer flow and aerodynamic performance of a finite forward-swept wing (NACA 0012 airfoil) were experimentally investigated. The Reynolds number and the forward-sweep angle were 2.5 x 10(4) < R < 10(5) and 0 degrees <= phi <= 45 degrees, respectively. The chord length was 6 cm, and the semiwing span was 30 cm; therefore, the semiwing aspect ratio was 5. The boundary-layer flow structures were visualized using the surface-oil-flow technique. Seven boundary-layer flow modes were identified by changing R, alpha, and phi: separation, separation bubble, secondary separation, leading-edge bubble, three-dimensional (phi = 0 degrees)/bubble-extension flow, and bluff-body wake modes. Furthermore, a six-component balance measured the aerodynamic loadings. The aerodynamic performance related closely to the boundary-layer flow modes. The dimensionless bubble length (L-b/C) indicated that a high forward-sweep angle conducted a longer bubble length than that at a low forward-sweep angle. The pseudostall occurred in the bubble-extension mode, while phi = 30 degrees, and alpha(stall) of 19.5 degrees at phi = 45 degrees was about 1.16-fold larger than that of 9 degrees at phi = 0 degrees as R = 8.0 x 10(4). Namely, the forward-sweep angle retards the stall. DOI: 10.1061/(ASCE)AS.1943-5525.0000144. (C) 2012 American Society of Civil Engineers.