Behaviour of spiral vortices on a rotating cone in axial flow

Experimental results are presented from a study of the boundary layer transition process and the behavior of spiral vortices in the transition range of the boundary layer on a 30 deg cone, rotating in axial flow. The trials were carried out with high speed photography of two rotating cones and hot wire anemometry. The apex of a rotating cone faced upstream. The laminar boundary layer was found to become unstable because of the presence of spiral vortices. The vortices were produced by centrifugal forces within the boundary layer and near the wall, in a thin region with steep velocity gradients. The vortices were distorted by the mean velocity field as they grew, and eventually sheared off.