Abstract
Flow behavior of leading edge vortices on a slender, 75° sweep-angle delta wing is studied experimentally in a water towing tank facility. The Reynolds number, based on root chord and free-stream velocity, is 9,000. Dye flow visualization and Particle Image Velocimetry (PIV) technique are used. From the instantaneous PIV measurement, a quasi-periodic shedding of KelvinHelmholtz type eddies from the separated shear layer is detected. The emergence of these sub-vortices is linked to the ejection of the secondary vortex as a result of the primary vortex/surface interaction. Along the vortex axis, the axial velocity distribution changes from a jet type profile to a wake type profile when vortex breakdown occurs. The corresponding azimuthal vorticity field switches its sign upstream of the vortex breakdown location. Instantaneous PIV data show that the spiral type vortex breakdown is dominant and the spiral of the vortex line is in a sense that is opposite to that of the base flow and it rotates in the same direction as the flow.
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