A computational approach is described for the rapid and systematic prediction and evaluation of the onset of dynamic stall due to rapid incidence changes or unsteady pitch or plunge motions. The method combines an unsteady, two-dimensional panel code with a two-dimensional boundary layer code. The panel code provides incompressible, inviscid owwelds about arbitrary airfoils undergoing prescribed motions. The boundary layer code computes laminar, transitional and turbulent regimes, with transition onset predicted by Michel's criterion. Presented results demonstrate that the delay in dynamic stall onset is directly related to the dynamic pressure lag, in agreement with previous Navier-Stokes simulations, but in apparent disagreement with several aspects of thèmoving wall' analogy suggested in the past as an explanation for delayed dynamic stall onset. Nomenclature c = chord length C p = pressure coeecient, (p ? p 1)=q 1 h = plunge amplitude in terms of c k = reduced frequency, 2fc=V 1 p = pressure q 1 = freestream dynamic pressure, 1=2 1 V 2 1 R L = chord Reynolds number, V 1 c== 1 t = time U = tangent velocity in the boundary layer U e = boundary layer edge velocity V 1 = freestream velocity x p = chordwise pivot location z() = plunge displacement, positive downward = angle of attack, positive clockwise = phase angle between pitch and plunge 1 = freestream kinematic viscosity 1 = freestream density = nondimensional time, tV 1 =c y NRC Research Associate z Professor, Fellow, ASME This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.
Download Full PDF Version (Non-Commercial Use)