Instantaneous three-dimensional vorticity measurements in vortical flow over a delta wing

An attempt is made to explore the structures in the vortical flow over a delta wing by spatio-temporal measurements of velocity vectors and subsequent evaluation of vorticity vectors. A novel probe, with good spatial resolution, to measure the multipoint velocity vector has been designed and constructed. Tests results of the statistical properties from the measurements of instantaneous velocity and vorticity vectors in the turbulent boundary layers gave confidence to investigate the vortices over a 45-deg-swept-back delta wing and to explore their complex structure with this probe. The present measurements indicated the existence of discrete stationary vortices in the feeding shear layer region as well as a primary vortex where mean vorticity is at maximum and where the mean velocity excess is about 1.3U(0). Large vorticity fluctuations, of the order of three to six times the mean vorticity, were measured between the low speed side of the shear layer and the surface of the delta wing. Such fluctuating vorticity statistics are presented for the first time. The shear layer reattachment zone and the region of secondary separation are associated with intense turbulence activities. It is also shown for the first time that secondary vorticity of alternating sign is generated at the wall of the delta wing through measurements of time-and space-resolved wall vorticity flux.