TOPOLOGICAL ANALYSIS OF THE VORTEX BREAKDOWN IN A CLOSED CYLINDER WITH A ROTATING LID

Key words: vortex breakdown, cylinder Abstract. In this paper the vortex breakdown phenomenon of the rotating flow within a closed cylinder with an instationary rotating lid is considered by calculating the viscous and laminar internal cylinder flow solving the unsteady Reynolds Averaged Navier Stokes equations. Thereby the rotation speed of the lid is linearly increased, which causes a gradual transition of the internal flow from a flow without any reversed flow at the vortex axis to a flow with one or more vortex breakdown bubbles. Later on the vortex breakdown bubbles disappear again. One research topic is to describe the transition phenomenologically using a simple visualization technique based on the magnitude of axial velocity and streamline integration. Beyond that a topological analysis has be done to get an impression of the main flow structures, their behaviour and changings. This is done by an advanced search for critical points of the velocity field both locally and in time. At these singular points the velocity magnitude vanishes and a structural change becomes obvious. The birth of critical points of the velocity field marks the beginning of the vortex breakdown in place and time and allows to compare the topological changings of different vector fields locall