Velocities on two-dimensional closed and semi-infinite aerofoils at zero incidence

Abstract

An attempt is made to clarify the position as to the comparative two-dimensional velocity distributions on a thin doubly symmetrical aerofoil and on the corresponding semi-infinite body, the front part being the same in the two cases. It is shown that the approximate linear method may be used with advantage to investigate the problem. The method provides a simple general proof that the supervelocity at the mid-chord station of a closed doubly symmetrical profile of any shape is approximately halved when the rear half is replaced by a semi-infinite parallel body. No such simple relationship applies to the entire chordwise distribution on the front part. All exact solution of the velocity distribution has been obtained for one particular semi-infinite profile and several alternative examples have been studied by the linear method. It is found that the ratio of maximum supervelocities may often considerably exceed 0.5 and sometimes rise to nearly 1.0.