Studies of Vortex Breakdown and its Stability in a Confined Cylindrical Container
A combined experimental and numerical study on vortex breakdown structure and its dynamic behavior in a confined cylindrical container driven by one rotating endwall has been performed. The experiments included flow visualization and hot-film measurements, and the numerical simulation included the solution by solving axisymmetric and the three-dimensional Navier-Stokes equations. The thesis offers detail investigations on the following specific issues: spiral vortex breakdown structure, mode competition between two axisymmetric limit cycles, vortex breakdown oscillation control and effects of modulation of the rotating endwall on the flow state. The experiment confirms the existence of an S-shape vortex structure and a spiral-type vortex breakdown. For the study on mode competition in the neighborhood of a double Hopf point, our experiments provide, for the first time, the laboratory evidence of the existence of an axisymmetric double Hopf bifurcation, involving the competition between two coexisting axisymmetric stable limit cycles. For the study of harmonic modulation, the experimental and numerical results show that the modulations can either enhance the oscillations of the vortex breakdown or quench them.
Vortex breakdown, stability, flow visualization, hot-film measurement, bifurcations, modulation
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