Abstract:Aerospace Systems, Inc. (ASI) conducted a study of dynamic stall in order to define its influence on the airfoil force and moment coefficients so that these effects can be included in the calculation ...Aerospace Systems, Inc. (ASI) conducted a study of dynamic stall in order to define its influence on the airfoil force and moment coefficients so that these effects can be included in the calculation of small wind energy conversion system (SWECS) loads and response. The effort includes a review of past work to determine its applicability to SWECS requirements, a definition of a dynamic stall theory for use in SWECS design, and computer implementation of the theory in SWECS loads and dynamic response analyses. Sample calculations are made for representative vertical-axis (VAWT) and horizontal-axis (HAWT) wind turbines. The basic results for the fixed-pitch HAWT show that dynamic stall effects may increase normal loads and moments by about ten percent. For the cyclic pitch VAWT, the peak normal load may be slightly underestimated but the peak moment may be significantly underestimated. The consequences of dynamic stall may be a change in performance with resultant mismatch of selected components or a reduction in the fatigue life of the SWECS structure. Semiempirical methods are used for the practical estimation of the forces and moments on oscillating airfoils or airfoils in an oscillating airstream. The dynamic stall method presented in this report is applicable primarily to large amplitude oscillations of the airfoil. Fully-developed dynamic stall is presumed and, therefore, the method may not be adequate for predicting aerodynamic loads and moments for incipient or light stall.Read More