Load alleviation of rigid and flexible wings in bluff-body wakes

Abstract The effectiveness of finite-span leading-edge mini-spoilers for separation control and trailing-edge spoilers for circulation control was investigated by means of wind tunnel experiments for alleviating the maximum aerodynamic loads experienced by both rigid and flexible wings in circular cylinder wakes. Periodic vortex shedding from circular cylinders was used to simulate flight scenarios involving encounters with periodic traveling gusts. Both wings had the same rectangular planform with a NACA0012 profile and a semi-aspect ratio of sAR = 5. Lift, wing root bending moment, flow fields, and flexible wing surface deformation measurements were taken at a chord Reynolds number of 300,000 at the pre-stall geometric angle of attack regime of α = 0–10°. Though there was no meaningful reduction in the maximum aerodynamic loads acting on the rigid wing at small α with a leading-edge spoiler for separation control, the lift reduction increased with α and a reduction of Δ C L,max ≈ − 0.235 was achieved at α = 10°. In contrast, the circulation control by a trailing-edge spoiler resulted in nearly constant reductions of up to Δ C L,max ≈ − 0.17 within the angle of attack range tested in the present study. For the flexible wing, the leading-edge spoiler led to reductions of up to 44% in the C L,max with little variations with α . While the trailing-edge spoiler resulted in larger reductions of up to 63% in the C L,max of the flexible wing at small α , the percentage reduction in the C L,max decreased rapidly as α increased. For both rigid and flexible wings, the efficacy of both spoilers reduced significantly with increasing wake gust amplitude. For the same wake gust amplitude, however, the leading-edge spoiler led to reductions in the twist angle, therefore the effective angle of attack, of the flexible wing, and as a result, it exhibited greater reductions in the maximum loads than the rigid wing. It appears that the performance of the spoilers was dictated by intermittent flow separations and subsequent reattachments over the wings under wake gusts.