Effect of Sweep on a Pitching Finite Wing

An investigation was performed into the effect of positive and negative sweep angle on the boundary layer transition and dynamic stall behaviour of a finite wing. The finite wing had a 6:1 aspect ratio, modern (SPP8) tip shape and positive twist, moving the maximum load on the wing away from the wind tunnel wall. Experiments were performed with sweep A=±30° and A=0° for static polars and sinusoidal pitching. The positively twisted wing shows a similar S-shaped boundary layer transition on the pressure side to that previously seen for helicopter rotor blades in hover. The transition positions on the suction side of the wing are comparable for the same local angle of attack at all values of the sweep L at each of the three pressure sections, and for dynamic pitching motions a hysteresis around the static transition positions is seen. Sweeping the wing led to later stall and higher maximum lift for both static polars and dynamic stall, except for a single case. The negative aerodynamic damping is worse for the swept wing than for the unswept wing, except where the delay of stall led to the flow remaining attached.