Preliminary Measurements of the Distribution of the Velocity of a Fluid in the Immediate Neighbourhood of a Plane, Smooth Surface

Abstract

It is generally known that if a fluid moves along the surface of a rigid body, the motion of the fluid in the vicinity of this surface will be retarded by the action of the frictional forces. The layer of fluid immediately in contact with the surface will adhere to the latter, and so, the body being supposed at rest, its velocity will be zero; the adjacent layers have velocities increasing with the distance from the surface, and a layer of a certain thickness has to be passed before the velocity acquires the value which is determined by the gradient of the pressure. This region of retarded motion (i.e. of motion retarded by the influence of the frictional forces) is called “boundary layer”, the conception of which has been introduced by Prandtl in 1904 ¹).