On the Prediction of Dynamic Stall Onset on Air- Foils in Low Speed Flow

1. Abstract 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. 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. Also, results are presented showing the eeect of airfoil shape and Reynolds number on the onset of dynamic stall. 2. Nomenclature c = chord length C p = pressure coeecient, (p ? p 1)=q 1 f = frequency in Hz k = for ramp motion: nondimensional pitch rate, 2== c for oscillating motion: reduced frequency, 2fc=V 1 p = pressure p 1 = freestream 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 = angle of attack, positive clockwise This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.