Anomalous flow phenomena due to breakdown of tip leakage vortex in an axial compressor rotor at near-stall condition

Abstract

Anomalous flow phenomena in an axial compressor rotor at near-stall conditions have been investigated by unsteady three-dimensional Navier-Stokes flow simulations. The simulations show-that the spiral-type breakdown of the tip leakage vortex occurs inside the rotor passage at the near-stall conditions. Downstream of the breakdown onset, the tip leakage vortex twists and turns violently with time, thus interacting with the pressure surface of the adjacent blade. The vortex breakdown causes significant changes in the nature of the tip leakage vortex, which result in the anomalous phenomena in the tip leakage flow field at the near-stall conditions: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing wall pressure trough corresponding to the leakage vortex, large spread of the low-energy fluid accumulating on the pressure side, and large pressure fluctuation on the blade pressure surface. As the flow rate is decreased from the near-stall conditions, the movement of the tip leakage vortex due to the vortex breakdown becomes so larger that the leakage vortex interacts with the suction surface as well as the pressure one. The interaction gives rise to the three-dimensional separation of the suction surface boundary-layer.