Boundary layer effects on airfoil lift

Abstract

A study of the discrepancy in lift between potential flow calculations and experiments was made. In potential flow the fluid is assumed to follow the contour of the airfoil, forming a stagnation point at the geometric center of the trailing edge. In the flow of a viscous fluid around an airfoil a boundary layer forms along the surface of the airfoil changing its effective shape. The pressure at the trailing edge is approximately equal to the static pressure at upstream infinity. Detail stagnation and static pressure and flow direction surveys were made near the trailing edge on a 50 inch chord NACA 0015 airfoil with trailing edge thickness increased to three per cent chord. By the use of thin airfoil theory, modified to include terms. of second order, good agreement with published experiments in lift and pressure distribution is obtained. Using Teledeltos paper, an electrical analog of the flow around the NACA 0015 airfoil in the tunnel was made. A method was developed for determining velocity directly from the analog.