Return from Aerofoil Stall During Ramp-Down Pitching Motions

This paper considers the unsteady reestablishment of fully attached flow of an airfoil from the stalled condition while undergoing ramp-down motions. The main purpose of the work was to extend the applicability of the Leishman-Beddoes dynamic-stall model during the return from stalled state to the low Mach and Reynolds numbers of the Glasgow unsteady database. This was done by the adoption of the Beddoes modeling philosophy and the technique of the lagging angle of attack that Sheng et al. [A New Stall-Onset Criterion for Low Speed Dynamic-Stall, Journal of solar Energy Engineering, Vol. 128, Nov. 2006, pp. 461-471; and Improved Dynamic-Stall-Onset Criterion at Low Mach Numbers, Journal of Aircraft (to be published)] proposed for developing a new dynamic-stall onset criterion. It is concluded that a more secure assessment was obtained of the nondimensional time taken to convect the stalled flow over and away from the airfoil, compared with those of Niven et al. (Analysis of Reattachment During Ramp Down Tests, Vertica, Vol. 13, No. 2, 1989, pp. 187-196) and Green and Galbraith (Dynamic Recovery to Fully Attached Aerofoil Flow from Deep Stall, AIAA Journal, Vol. 33, No. 8, 1995, pp.1433-1440). This, combined with the appropriate lift-curve slope, yielded an improved data reconstruction over that of the Leishman-Beddoes model. The present depiction and modeling of the reestablishment of fully attached flow from stalled state is a valid enhancement to the Leishman-Beddoes model.