Effect of Tunnel Walls on Vortex Breakdown Location over Delta Wings
Vortex breakdown has been the subject of many investigations during the past few decades. Many of the investigations were performed by visualizing the vortical flowfield above delta wings in water or wind tunnels. In spite of the extensive use of this technique, little attention has been paid to the possible influence of the test section walls on the measured location of the vortex breakdown. The present work suggests a possible model by which the walls may affect the vortex breakdown location. The suggested model is associated with the upwash induced on the wing surface due to the presence of the walls. This upwash was found to be relatively small near the wing's apex and larger on the trailing edge, thus creating an effectively cambered wing. The effective camber tends to shift the vortex breakdown location downstream as compared to a flat wing with the same projected geometry. The influence of the walls was tested in a series of experiments in a water tunnel using delta wings with different sizes, relative to the test section dimensions. The anticipated trend was observed in the experimental results. Nomenclature Cr = wing root chord length H = test section height V = undisturbed velocity S =wing span W = test section width Xbd - vortex breakdown location along the wing root chord a = angle of attack ALE = leading-edge sweep angle