DYNAMIC AIRFOIL FLOW SEPARATION AND REATTACHMENT

An analysis has been performed of existing theoretical and experimenta l results to determine the flow physics responsible for the observed d elay of flow reattachment to a negative flow incidence in a modestly r apid pitch-down motion of an airfoil. It is found that the responsible flow physics are essentially the same as those causing dynamic oversh oot of static lift maximum in pitch-up motions, i.e., the accelerated now and moving wall effects, The analysis shows that the dominant role played by the moving wall effect during pitch-down motions is in agre ement with existing experimental results for a rotating circular cylin der. Applying the moving wall effect, measured through the Magnus lift on a rotating circular cylinder, to an airfoil describing pitch-down motions produces predictions that are in good agreement with experimen tal results. A thorough understanding of this moving wall effect is re quired for prediction of the high-alpha unsteady aerodynamics of advan ced aircraft.