Passive flow control over flexible non-slender delta wings

Force measurements over a range of non-slender delta wings have demonstrated the ability of a flexible wing to enhance lift and delay stall compared with a rigid wing of similar geometry. The work has extended the results of a recent study to include delta wings with a range of sweep angles. It has been shown that the greatest lift enhancement was observed over the wing with smallest leading edge sweep. Additionally for the only slender wing considered no lift enhancement was observed indicating that it is a feature of the fundamentally different flow that occurs over low-sweep wings that is responsible for the phenomenon. The variation of RMS lift force and rolling moment coefficients with incidence for all the wings concerned suggest that the wings are vibrating in an antisymmetric structural mode in the lift enhancement region. This supports previous evidence for the 50° wing that suggests the same. Further, experiments of a half-wing model suggest that this wing does not undergo lift enhancement, and as such it may be that the antisymmetric vibration is a necessary condition for the lift enhancement to exist. Wing-tip deflections for some of the wings were also measured, which showed that the slender wing undergoes much higher time-averaged deflections than the non-slender wings, although it also experiences a much lower level of buffet. PIV and LDV measurements have demonstrated the striking difference between the surface flows over the flexible and rigid wings in the post-stall region at the same incidence. Implementing flexibility on a low sweep wing results in continued reattachment of the shear layer to much higher incidences than would otherwise be observed over a rigid wing.