Instabilities of the flow between a rotating and a stationary disk

Abstract

This experimental study is devoted to the description of the different patterns resulting from instabilities which appear in the flow between a rotating and a stationary disk enclosed by a stationary sidewall. With the help of visualizations we describe the different flow regimes as functions of two control parameters: the Reynolds number and the aspect ratio of the gap separating the disks, which are varied over large continuous ranges. Moreover, visualizations and ultrasonic anemometry lead to the description of the different instabilities and to the construction of a transition diagram that summarizes the domains of existence of the various patterns. Two different scenarios of transition are mainly followed by the flow. When the gap between the two disks is more than the thickness of the two disk boundary layers, circular and spiral waves destabilize the stationary disk boundary layer. Transition occurs in this case by the mixing of these waves. On the other hand, when the two boundary layers are merged, finite-size turbulent structures can appear. They consist of turbulent spots or turbulent spirals which invade the laminar domains as the Reynolds number of the flow is increased.