Unsteady Separation Processes and Leading Edge Vortex Precursors: Pitch Rate and Reynolds Number Influences

A NACA 0015 airfoil was pitched at constant rate through static stall to elevated angles of attack. Time-dependent shear stress measurements were performed near the airfoil leading edge. Using these data, unsteady boundary layer processes preceding leading edge vortex emergence were characterized for a broad range of nondimensional pitch rate and Reynolds number. In addition, steady data were acquired and examined to furnish a baseline for analysis and comparison. Overall, the analyses revealed a progression of events culminating in leading edge vortex emergence. Analyses allowed the independent influences of nondimensional pitch rate and Reynolds number upon this progression to be ascertained and inferences to be drawn regarding the structure of the resulting local flowfield