Experimental Investigation of the Parallel Vortex-Airfoil Interaction at Transonic Speeds

Unsteady vortex-airfoil interaction experiments at transonic Mach numbers ranging from 0.7 to 0.85 and airfoil chord Reynolds numbers of 3.5 X 106 to 5.5 x 10 6 were conducted in the University of Texas at Arlington high Reynolds number transonic wind-tunnel facility. The experiments were designed to simulate a two-dimensional blade-vortex interaction problem frequently encountered in rotocraft applications. The interaction experiments involved positioning a two-dimensional vortex generator upstream of a NACA 0012 airfoil section and impulsively pitching the vortex generator airfoil such that the starting vortex interacts with the downstream airfoil. The vortex generator was pitched about its 0.25 chord position with nondimensional pitch rates in the range of 0.004-0.008. Experiments were conducted at several vortex core positions above and below the downstream airfoil. The results indicate a substantial change in the pressure distribution over the leading 30% of the interacting airfoil. Experimental data for Mach numbers representing supercritical flows over the airfoil resulted in a very strong interaction of the vortex and the airfoil shock wave; at close encounters, these interactions resulted in unsteady local flow separation of the leading 40970 of the airfoil chord. Experiments with stronger vortices at supercritical Mach numbers resulted in a forward propagation of the shock wave. The pressure distribution of the downstream airfoil was not sensitive to Reynolds number variations for the range of Reynolds numbers simulated in the test program.