Reduced frequency effect on an unsteady compressible boundary layer over an oscillating supercritical airfoil

Boundary layer states, including laminar, turbulent, attached or separated, have significant effects on an airfoil operation and aerodynamic forces; especially as the boundary layer becomes turbulent or separated, the drag forces increase significantly. In the compressible flow and the transonic regime, when the compressibility effects and shock–boundary layer interaction are also considered, the flow field is so complicated that it cannot be easily investigated using the theoretical and computational methods. In this study boundary layer is investigated experimentally in several static angles of attack and also, during sinusoidal pitching motions at M ∞ = 0.65, Reynolds number of 9.202 million per meter, using multiple hot film and pressure sensors. Transition and relaminarization points, supersonic region, and shock formation are detected on the upper surface of the airfoil, and, the reduced frequency effect is investigated in dynamic case. It is worth mentioning that the low-range oscillation amplitudes and reduced frequencies used in this research led to quite different and interesting results that have not been considered in the other investigations dealing with oscillating airfoils.