Prediction of stall and post-stall in two- and three-dimensional flows

Abstract

An efficient and accurate calculation method for the prediction of stall and post-stall of twoand three-dimensional high lift configurations is presented. The method is based on the interactive solution of the inviscid flow and boundary layer equations. The efficiency and robustness of the method have been improved by linearizing the turbulent terms in the boundary layer equations. Also, a model for surface roughness has been incorporated. The method is applied to the calculation of lift and drag coefficients about twoand threedimensional configurations up to stall and poststall conditions. Results show that the method predicts correctly the effects of Reynolds number and surface roughness on airfoil stall. For three-dimensional flows, the Reynolds number effects are also predicted. The paper shows the importance of an accurate calculation of wake flows for the prediction of the stall of three-element wings. In both twoand threedimensional flows, the effects of Mach number are captured, provided the flow remains well below sonic conditions. In the contrary, a compressible inviscid flow method should be used in lieu of the panel method used here with compressibility corrections. required combination of accuracy and robustness is for the prediction of stall and post-stall of high lift configurations. The necessity of obtaining multiple solutions in a fast paced design environment further enhances the challenges facing the CFD community. In fact, even when the current growth rates in computer power are extrapolated, the direct numerical simulation (DNS) of three-dimensional high lift configurations is several decades away. Therefore, alternatives which meet both accuracy and efficiency requirements must be developed for use in aircraft high lift design.