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.