Calculation of the displacement effect in two-dimensional subsonic attached flow around aerofoils: examples of calculations using measured displacement thicknesses

Abstract

Using measured displacement thicknesses the classical displacement effect on lift and pressure distribution has been calculated for a number of aerofoils in viscous attached flow. For this purpose the displacement concept boundary condition (in its "leak flow" form) has been incorporated in a potential flow calculation method that uses a discretized surface singularity distribution. Comparisons between results of the present calculations and experimental values of lift confirm the earlier findings of Preston (1953) and Spence (1954) that the classical displacement concept tends to underestimate the total viscous lift loss especially in cases with large trailing edge angle. This illustrates the need for the possibility to take more appropriate care of the singular behaviour of the flow near the trailing edge.