Flow Patterns and Aerodynamic Performance of Unswept and Swept-Back Wings

Abstract

The effects of sweep-back angle (Λ), Reynolds number (Re), and angle of attack (α) on the boundary-layer flow structures and aerodynamic performance of a finite swept-back wing were experimentally investigated. The Reynolds number and sweep-back angle used in this test is 30,000<Re<130,000 and 0 deg≤Λ≤45 deg. The wing model was made of stainless steel, and the wing airfoil is NACA 0012. The chord length is 6 cm, and the semiwing span is 30 cm; and therefore, the semiwing aspect ratio is 5. The boundary-layer flow structures were visualized using the surface oil-flow technique. Seven boundary-layer flow modes were categorized by changing Re and α. A six-component balance is used to determine aerodynamic loadings. The aerodynamic performance is closely related to the boundary-layer flow modes. The stall angle of attack (αstall) is deferred from 9 deg to 10 deg (for an unswept wing), to 30 deg to 35 deg (for a swept-back wings of Λ>30 deg). The deferment of αstall is induced from the increased rotation energy and turbulent intensity generated from the secondary flow. Furthermore, the increased rotation energy and turbulent intensity resisted the reverse pressure generated at high α.