Experimental investigation of the perpendicular rotor blade-vortex interaction at transonic speeds

Transonic perpendicular rotor blade-vortex interaction (BVI) tests at Mach numbers ranging from 0.68 to 0.9 and Reynolds numbers (based on the airfoil chord) of 3.8-5.5 million were conducted in the UTA high- Reynolds number, transonic Ludwieg-tube wind tunnel. The scheme involved positioning a lifting wing (vortex generator) upstream of an instrumented NACA 0012 airfoil so that the trailing vortex interacted with the downstream airfoil. Tests were performed at several vortex strengths as well as several vortex core heights above the downstream airfoil. The results obtained from these experiments indicate that a substantial change in the pressure distribution of the downstream airfoil occurs, but most of the effects were confined to the leading 30% of the airfoil chord. A spanwise drift of the vortex core as it passes over the trailing airfoil, similar to results observed previously in low-speed wind tunnel tests, as well as a high degree of unsteadiness in the vicinity of the vortex center were observed.