MEASUREMENTS OF CIRCULATION AND VORTICITY IN THE LEADING-EDGE VORTEX OF A DELTA-WING

Cross-wire measurements of the flowfield above a 75-deg flat plate delta wing were performed at a centerline chord Reynolds number of 2.5 X 10(5). Surveys normal to the planform yielded velocity field data at incidence angles of 20 and 30 deg for a series of chordwise locations. The distribution of the velocity, axial vorticity, and circulation showed a strong conical behavior upstream of the breakdown region and away from the apex and trailing edge regions. Spanwise velocity and vorticity profiles through the core of the vortex upstream of breakdown were scaled with the local geometry. Prior to breakdown, the majority of the axial vorticity in the primary vortex was observed to be concentrated at the center of the vortex, in a region of about twice that of the subcore diameter. The influence of changes in the angle of attack on axial vorticity with the opposite sense, such as that found in the secondary vortex, was much less than the vorticity in the primary vortex. The growth of the vortex circulation with distance from the apex was approximately linear over the forward end of the planform. The rate of growth was observed to decrease, however, aft of the midchord location. Radial circulation distributions scaled with the local semispan and exhibited a logarithmic behavior with increasing distance from the subcore, implying the possibility of a strong dependence on the local Reynolds stresses. Finally, parameters derived from slender body theory are shown to correlate the circulation for wings of different sweep.