Incompressible Flow About an Airfoil

Abstract

The physical characteristics of external flow past a thin airfoil at a small angle of attack enables us to build a simple mathematical model of the flow. We assume here our profile starts to move impulsively from the rest and reaches the constant speed of U in zero time. If the viscous forces exist, their resistance to the impulsive motion will be so large that the required force to move the airfoil will also be incredibly large. However, if we neglect the viscous effects at the beginning, the assumption of impulsive start of a motion will be more meaningful. Under this assumption, we can model the external flow in connection with the creation of lift via the bound vortex formation around the airfoil in a free stream and explain the whole phenomenon by means of Kelvin’s theorem which was introduced in Chap. 2.