Effects of Tip Leakage Vortex Breakdown on Flow Field in Turbomachinery Blade Row

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The tip leakage vertex rolled up near the leading edge takes on the spiral-type breakdown in the fore part of the rotor passage at the near-stall conditions. The onset of the leakage vortex breakdown causes the drastic changes in the nature of the leakage vortex: downstream of the breakdown onset, the leakage vortex twists and turns violently with time, and has no feature of the streamwise slender vortex. The large movement of the leakage vortex gives rise to a strong interaction of the leakage vortex with the pressure surface of the adjacent blade. Although the interaction causes no separation of the blade boundary layer, the effects of the leakage vortex breakdown play a major role in the unsteady flow nature near the rotor tip at the near-stall conditions.The spiral-type breakdown of the tip leakage vortex brings about the anomalous flow phenomena in the 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 pressure side.As the low rate is decreased further from the near-stall conditions, the movement of the tip leakage vortex due to its 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 near the tip. As a result, the total pressure rise across the rotor decreases drastically. It is found that the stall in the compressor rotor can be caused by the effect of the leakage vortex breakdown.