Vortex flows on a rolling nonslender delta wing

An experimental investigation of a nonslender delta wing, with a 50° leading edge sweep, was conducted in order to understand the unsteady vortical flows during a dynamic rolling motion. Dye flow visualization and DPIV (Digital Particle Image Velocimetry) measurements were conducted in a water tunnel study. When vortex breakdown was present over the wing at zero roll angle, its variation was little affected at static or dynamic roll angles. However, there were relatively large variations of maximum vorticity and in the size of the vortical flow region in a cross-flow plane. In the static case, when vortex breakdown was at the apex of the wing at zero roll angle, a coherent vortex was formed and vortex breakdown could be observed over the wing for large roll angles. In the dynamic case, even for small dimensionless frequencies, there were coherent leading-edge vortices on both sides of the wing throughout the whole cycle, rather than partially or completely stalled flow as in the static case. However, the variation of breakdown location over a cycle was much smaller. When the dimensionless frequency of the rolling motion was substantially increased, the amplitude of cyclic variations in breakdown location decreased. In addition, hysteresis increased with increasing frequency, and was most noticeable at zero roll angle. The existence of multiple vortices with the same sign of vorticity as the primary vortices was apparent at some roll angles. Variation of circulation also showed hysteresis and had certain similarities to the variations of breakdown location, although the magnitudes of these variations were much larger.