Abstract

A technique of illuminating a section of the flow which has13; become very popular recently uses a sheet of light obtained by expanding a laser beam by passing it through a cylindrical lens system . This report gives the results of first application of this technique in NAL. A delta wing of aspect ratio 0 .53 was placed in the NAL boundary layer tunnel at various incidences upto 35 0 and sideslip angles upto 20 0 . The freestream speed was 3m/s, the chord Reynolds number being 0 .53 x 105 quot;. Smoke was introduced upstream of the apex of the wing model . Vertical planes at 40% to 75% of chord were illuminated by the laser sheet by traversing the laser . The cross-sections of the flow within the vortices above the delta wing model and also downstream of the trailing edge were photographed . The pictures show sharp vortex cores changing into diffused cores over a relatively small distance . There is a secondary instability of shear layer visible in some photographs especially in the transition region .