The instability and transition of a boundary layer on a rotating cone. (4th report Cones of different total angles and effects of freestream turbulence)

Abstract

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 total included cone angles of 15°, 30° and 60° in a range of freestream turbulence (0.04% to 3.5%) using a hot-wire anemometer and a flow-visualization technique. The transition region is determined with the critical Reynolds number and the transition Reynolds number in relation to the rotational speed ratio. The spiral vortices are 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 the vortices increases with increased cone angle. These experimental results are compared with the present numerical results based on the linear stability theory. The freestream turbulence has no effect on the transition Reynolds number, while the effect becomes more sensitive to the critical Reynolds number as the cone angle is increased.