| Separated flow over the leeside of nonslender delta wings was studied experimentally. A version of Stereo Digital Particle Image Velocimetry was applied to measurements in a low speed water tunnel, at Reynolds numbers below 20,000, for delta wing models of 50° and 65° leading edge sweep and 30° windward-side leading edge bevels. Measurements were taken over the starboard portion of the wing planform in crossflow planar slices near the apex region in the 5°–20° angle of attack range, yielding all three components of the velocity field, albeit restricted to planar cuts. These measurements were confirmed by flow visualization.; For the 50° wing, the primary leading edge vortices were stable below 10° angle of attack. The vortex breakdown region exhibited gradual and steady upstream progression with increasing angles of attack, from aft of the trailing edge to approximately the mid-chord. Secondary leading edge vortices were found to decay more abruptly, and at lower angle of attack than the primaries, all but disappearing by 10° angle of attack. This suggests a possible predictive criterion for breakdown of the primary vortices, at least at low Reynolds number. The entire vortex system undergoes large-scale instabilities in the 12°–20° angle of attack range, with a corresponding sharp drop in axial velocity in the primary leading edge vortex core. The leading edge shear layer, however, remains in an organized rolled-up state. By 20°, the flow over the leeward side of the wing is at the threshold of complete separation, with flow along the wing centerline stalling as the left and right separated regions merge.; Both wings exhibited a largely stagnant region outboard of the primary LEV and inboard of the leading edge shear layer, especially at angles of attack beyond 10°. This phenomenon is consistent with some prior observations at Reynolds numbers on the order of 20,000 and below.; The abruptness of the stall of the 50° wing and the close relationship between the leading edge vortex flow and the leeward surface boundary layer are qualitatively indicative of a transitional case from slender delta wing separation to classical airfoil stall. |
