A DETAILED EXPERIMENTAL ANALYSIS OF DYNAMIC STALL ON AN UNSTEADY TWO–DIMENSIONAL AIRFOIL

An experimental analysis of dynamic stall on an unsteady, two-dimensional, NACA 0012 airfoil is presented. Pressure, hot-wire, and smoke flow visualization data are correlated for test parameters representative of actual helicopter rotor operating conditions. These data reveal a number of interesting Reynolds number, amplitude, and reduced frequency effects on dynamic stall. A short laminar separation bubble is observed to precede stall, but there are not enough data to show the bursting of this bubble. The formation and shedding of a leading-edge vortex is documented, and its effects on dynamic stall are discussed. It is the intent here to point out the importance of testing under actual helicopter rotor operating conditions and that this approach can eventually describe the mechanism of dynamic stall.