Systematic wind-tunnel investigations of vortex breakdown have been conducted on sharpedged delta and modified delta wings with sweep angles from 45° to 85° at Reynolds numbers of about 1 X 10 6 , utilizing a schlieren system for flow visualization. Vortex breakdown positions are presented as a function of angle of attack and sweep. Lift measurements generally compare favorably with Polhamus' leading-edge suction analogy. Drag because of the lift is predicted quite satisfactorily as the streamwise component of normal force for all models tested. Effects of vortex breakdown on pitching moments are presented and discussed. Tests of the modified delta wings show that vortex breakdown is influenced much more strongly by planform changes near the apex than changes near the trailing edge.
Nomenclature
BD-vortex core breakdown c = wing local chord C = wing mean geometric chord, C 0 = wing reference chord (usually centerline)wing pitching moment coefficient about I mean aerodynamic chord, moment/#>SC K p , K v = constants in Polhamus' lift equation q = dynamic pressure S -wing planform area TE = trailing edge a = angle of attack
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