Experimental investigations of the vortex flow on delta wings at high incidence

It is reported in the literature that strongly asymmetric vortex flow occurs on the lee side of slender delta wings at high incidence, similar to that observed on slender cones, and a boundary is given for the onset of asymmetry vs wing aspect ratio. To study this phenomenon, dye flow-visualization tests were carried out on two slender, sharp-edged delta wings of aspect ratio A = 0.56 and 0.28 up to high incidences in a water tunnel. Another wing with A = 0.56 was studied in a wind tunnel, using a smoke flow-visualization technique. Reynolds numbers based on the root chord in the water tunnel and wind tunnel were Rec — 3.4 x 10 4 and 1.32 x 10 s, respectively. No strongly asymmetric vortex flow was observed in our tests before vortex breakdown occurred on the wing. Subsequent evaluation of flow observations reported elsewhere did not reveal strongly asymmetric vortex flow on slender wings of various planforms. One delta wing reported to exhibit strongly asymmetric vortex configurations; on closer study, it probably had near its apex the shape of something like a thick, elliptic cone, rather than that of a flat, thin delta wing. Theoretical results for inviscid flow past slender cones at incidence strongly suggest that on a thin delta wing no strongly asymmetric vortex flow occurs of the type found on slender, circular, or thick elliptic cones.