Acoustic and turbulence influences on stall hysteresis

P AST testing of airfoils at low Reynolds number has revealed stall hysteresis to be a characteristic of airfoil aerodynamic behavior at Reynolds numbers between about 75,000 and 500,000. This important phenomenon, has been seen by some researchers but not by others, and the extent of the loop has varied in results from different investigators. The purpose of this study was to investigate the extent to which wind-tunnel, flow turbulence and acoustic disturances may alter the nature of the flow over an airfoil at low Reynolds number and the character of the stall hysteresis loop. The results indicate that such disturbances may have dramatic effects on stall hysteresis and may be responsible for the lack of stall hysteresis data in many past investigations.