PITCH RATE AND REYNOLDS-NUMBER EFFECTS ON UNSTEADY BOUNDARY-LAYER-TRANSITION AND SEPARATION

A NACA 0015 airfoil was pitched at a constant rate through static stal l to elevated angles of attack, Shear stress measurements of high spat ial and temporal resolution were performed near the airfoil leading ed ge, in the vicinity of subsequent dynamic stall vortex initiation, Usi ng these data, unsteady boundary-layer reversal and transition were ch aracterized for a range of nondimensional pitch rates and Reynolds num bers. Analyses revealed the independent influences of nondimensional p itch rate anti Reynolds number upon unsteady boundary-layer reversal a nd transition, Temporal sand spatial relationships between unsteady bo undary-lager reversal and transition imply that unsteady boundary-laye r reversal is a precursor and principal determinant in unsteady bounda ry-layer transition, Comprehension of these and other fundamental unst eady flow physics are crucial For the control of dynamically-separated flows generated by maneuvering aircraft, rotercraft, and wind energy machines.