Circulation Control Airfoil Study: Progress Report No. 4

Abstract

The prime goal of the investigations has been the evaluation of the unsteady aerodynamics, and in particular the transfer functions, applicable to the Circulation Control Airfoil (CCA) for the situation of harmonic blowing perturbations superimposed upon a mean cavity pressure. Circulation control was achieved upon the relatively thick (t/c = 0.214) elliptically shaped two-dimensional air foil by tangential jet injection at an upper surface slot just ahead of the rounded trailing edge. The experiments were conducted in the Naval Postgraduate School unsteady flow 2 x 2 foot wind tunnel. Preliminary results were obtained disclosing the nature of unsteady surface pressures over the airfoil, both amplitude and phase, relative to the oscillating cavity pressures for a range of reduced frequencies, k=0 to 0.46, at a model attitude approximating the zero lift condition (blowing-off) at a moderate value of momentum blowing coefficient. Positive results were obtained towards identifying the behavior of the Coanda sheet dynamics, airfoil lift transfer function and airfoil damping moment