Vortex Structure on a Delta Wing at High Angle of Attack

Abstract

The structure of the leading-edge vortex from a delta wing at high angle of attack is addressed using a scanning laserversion of high-image-density particleimagevelocimetry.Emphasisis ontheglobal patterns of instantaneous vorticity.Thesepatternsarerelated to distributions ofaveraged and e uctuating velocity and vorticity. At low angle ofattack,intheabsenceofvortex breakdown,itispossibleto detecta totalofe vedistinctlayersofvorticity;theyall exhibit small-scale concentrations of azimuthal vorticity. Immediately downstream of thetrailing edgeof the wing, larger-scale vorticity concentrations appear in the outermost vorticity layers. At sufe ciently high angle of attack, vortex breakdown evolves from the innermost two vorticity layers. For all of these classes of vortical structures, the values of dimensionless wavelength and circulation are assessed. Moreover, the onset of vortex breakdown is interpreted in terms of both instantaneous and averaged patterns of velocity and vorticity. These considerations lead to a direct comparison of vorticity-based and stagnation criteria for breakdown. In turn, these criteria are linked to the onset of regions of e uctuating vorticity in the initial region of breakdown.