Turbulent and unsteady flow characteristics of delta wing vortex systems

This paper presents an overview of experimental investigations on a 65 deg swept delta wing as part of the International Vortex Flow Experiment 2 (VFE-2). Results obtained in low-speed wind tunnel facilities include oil flow and laser light sheet flow visualization, mean and unsteady surface pressure distributions as well as mean and turbulent velocity components of the flow field and close to the wing surface. Thus, field and near wall distributions of all components of the Reynolds stress tensor are available. Details of the delta wing vortex structure and breakdown phenomenon are discussed and analyzed. Vortex bursting leads to specific spectral densities of velocity and surface pressure fluctuations characterized by narrow band distributions associated with the helical mode instability of the vortex breakdown flowfield. Further, special emphasis is on the occurrence of an inner vortex detected for the low Reynolds number and Mach number regime. This inboard vortex results from a laminar separation close to the apex due to the spanwise pressure gradient in the area of relatively large thickness while the classical leading-edge vortex progressing from the rear part to the apex is fed from the turbulent shear layers shed at the wing upper and lower side.