An experimental study on vortex breakdown in a differentially-rotating cylindrical container

Abstract

The vortex breakdown phenomenon in a closed cylindrical container with a rotating endwall disk was reproduced. Visualizations were performed to capture the prominent flow characteristics. The locations of the stagnation points of breakdown bubbles and the attendant global flow features were in excellent agreement with the preceding observations. Experiments were also carried out in a differentially-rotating cylindrical container in which the top endwall rotates at a relatively high angular velocity Omega(t), and the bottom endwall and the sidewall rotate at a low angular velocity Omega(sb). For a fixed cylinder aspect ratio, and for a given relative rotational Reynolds number based on the angular velocity difference Omega(t)-Omega(sb), the flow behavior is examined as vertical bar Omega(sb)/Omega(t)veritical bar increases. For a co-rotation (Omega(sb)/Omega(t)0), the breakdown bubble is located closer to the bottom endwall disk. However, for a counter-rotation (Omega(sb)/Omega(t)<0), the bubble is seen closer to the top endwall disk. For sufficiently large values of Omega(sb), the bubble ceases to exist for both cases.