Some Transition Patterns in Axisymmetric Boundary Layers

Abstract

Direct observation of the vortex pattern caused by a ring-shaped trip is made on 1-in. and ½-in. circular cylinders and on a 30° cone in a water tank. Over the cylinders the boundary-layer thickness is approximately equal to the radius of the cylinders. Ring-shaped vortices are shed and deformed into vortex loops in the same manner as on a flat plate. On the cone the ring-shaped vortices are stretched and then inevitably deformed into vortex loops, indicating that a mere stretching is not a sufficient mechanism for the creation of a turbulence spot. A mechanism of the final breakdown from the vortex loop is tentatively proposed.