Boundary-layer transition on rotating cones in axial flow with free-stream turbulence

This paper is concerned with the laminar-turbulent transition of three-dimensional boundary layers on cones rotating in external axial flow. The experiment was carried out for three cone angles of 15°, 30° and 60° in a range of free-stream turbulence (0.04% to 3.5%) using a hot-wire anemometer and a flow-visualization technique. The transition region was determined with the critical Reynolds number and the transition Reynolds number in relation to the rotational speed ratio. The spiral vortices were found to fix relative to the rotating surface. The relation of the direction of the spiral vortices to the rotational speed ratio remains unchanged as the cone angle becomes larger, while the number of vortices increases with increased cone angle. These experimental results were compared with the present numerical results based on the linear stability theory.