Evolution of Delta Wing Surface Contour from Flat Plates to Boxfish: Effects of LEV Confinement

Both flat plate delta wings and tall boxfish shapes generate flow fields characterized by a pair of counterrotating LEVs. One can imagine a spectrum of shapes from a flat wing to a thick boxfish-like geometry in which the LEV is confined by the proximity of the lee-side wing surface. Several wing shapes from this distribution have been manufactured and investigated in a novel compact low speed water tunnel to probe the relationship between LEV confinement and on the leeside flow field and wing performance.

Fluorescent dye visualizations, stereo PIV, and load cell measurements indicate that raising the height of the leeward surface, effectively confining the LEV, leads to substantial reductions of LEV strength and changes in LEV position. The first evidence of a split dual-primary LEV structure is presented. Tomographic 3D reconstructions of the dye flow field reveal complex three-dimensional vortex behavior on the aft portion of the wings, including flow separation patterns reminiscent of those seen on hatchback cars and Ahmed bodies. Force measurements reflect the observed flow field, with highly non-linear force evolution with angle of attack depending on model cross-sectional and longitudinal profiles.