Laser-Doppler Velocimeter (LDV) Measurements of the Velocity Field of a Leading Edge Vortex over a delta Wing Before and after Vortex Breakdown

摘要

The results of velocity measurements in the flow field over a delta wing with aspect ratio 1.6 at angles of attack 19.3 deg and 28.9 deg are given. The experiments were performed with laser Doppler velocimetry in backscatter mode. Only 50% of maximum laser power was used. Measurements were made in a nonburst as well as in a burst vortex. The experiments were carried out in the L-2B low speed tunnel at free stream velocities of 18 m/s to 19.5 m/sec. The results are compared with theoretical calculations of the velocity distribution by Hall and Ludwieg and Ludwieg's stability theory of vortex breakdown. The assumption of a conical flow within the vortex was proved to be valid except near the trailing edge. The axisymmetry of the flow field could not be proved. Deviation of the measured velocity distribution from an ideal Hall vortex is probably due to vortex asymmetry.