Experimental investigation of the reduced frequency effects on a plunging airfoil near static stall region

Abstract

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.Details of pressure distributions and aerodynamic coefficients on a two dimensional plunging airfoil, at low speed wind tunnel are presented. Dynamic motion was produced by plunging the model over a range of reduced frequencies, and mean angles of attack. The Reynolds number in the present test was held fixed (R<>=1.5x1O5), and the reduced frequency was varied in almost wide range. During the oscillating motion, surface static pressure distribution was measured on the upper and lower side of the model. The aerodynamic loads were calculated from the surface pressure measurements. The flow structure was studied in stall onset region. The hysteresis loops of pressure coefficient and aerodynamic loads showed that the reduced frequency had important effects on the unsteady behaviors of the flow. Near static stall angle of attack, an energetic vortex structure at the airfoil leading edge was formed. This dynamic vortex allowed the airfoil to achieve much higher lift coefficients before significant separation occurred.