VII. An investigation of the air-flow pattern in the wake of an aërofoil of finite span

Abstract

1. The earliest physical conception of the flow in the wake of an advancing aërofoil of finite span was suggested by Lanchester, who showed, from theoretical considerations, that it should comprise a layer of vorticity immediately behind the trailing edge and two general circulatory motions of opposite direction of rotation, one at each aērofoil tip. Since that time, photographs of this circulatory motion of air at the aërofoil tips have been taken by Caldwell and Fales, and other experimenters have located, by direct measurement, regions of vorticity in the wake, principally behind the aërofoil tips. The purpose of the present investigation is to obtain, by precise measurements of the wind speed and direction, a more complete picture than has hitherto been available of the disturbance behind an aërofoil of finite span, and to map out the changes which occur in the extent and distribution of the vorticity in the wake as it passes down-stream. The measured vorticity is considered in relation to the circulation around the aërofoil, and from this point of view the work herein described may be regarded as a continuation of that undertaken by L. W. Bryant and D. H. Williams,|| who confirmed experimentally the Kutta-Joukowsky relation connecting circulation and lift.