Theoretical Predication of Airfoil Drag Polars

A computer program has been developed which can faithfully reproduce certain viscous flow phenomena which up to now have defied analysis. The foundation of this program is rooted in a better understanding of the boundary layer development over a two-dimensional body. The use of an existing laminar boundary layer theory, in conjunction with an improved transition criteria and turbulent boundary layer theory, has led to a capability of predicting the complete boundary layer development on an airfoil section given only the pressure distribution about the body. The theoretical trailing-edge values of the momentum thickness, θ, and shape factor, H, are used in the Squire and Young profile drag formula to calculate the section drag coefficient. The lift coefficient, obtained from integrating the pressures used in the boundary layer analysis, are plotted against the section drag coefficient to obtain the airfoil drag polar. The results of the theory will be compared with experimental airfoil drag polars as obtained by the NACA. Further uses of this new theory, such as predicting the effect of Reynolds number on the section drag polar, the variation of section skin friction coefficient with angle-of-attack, and the effect of Reynolds number on maximum section lift coefficient, will be demonstrated.