The motion of a thin oil sheet under the steady boundary layer on a body

A solution is obtained for the motion of a thin oil sheet, of non-uniform thickness, under a boundary layer. The following points are deduced: ( a ) The oil flows in the direction of the boundary-layer skin-friction, except near separation, where the oil tends to indicate separation too early. These conclusions are independent of oil viscosity. ( b ) The effect of the oil flow on the boundary-layer motion is very small. The application of the results to the interpretation of oil-flow patterns is briefly considered.