Stewartson layer

In fluid dynamics, a Stewartson layer is a thin cylindrical shear layer that connects two differentially rotating regions in the radial direction, namely the inside and outside the cylinder. The Stewartson layer, typically, also connects different Ekman boundary layers in the axial direction. The existence of such layer was first noted by Ian Proudman, while its structure was first described by Keith Stewartson. This layer should be compared with the Ekman layer which occurs near solid boundaries.