Rotating Stall Inception Due to Breakdown of Tip Leakage Vortex in Compressor Rotors

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The unsteady flow nature caused by the breakdown of the tip leakage vortex in an axial compressor rotor at near-stall conditions has been investigated by unsteady three-dimensional Navier-Stokes flow simulations and by experimental measurements. 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 motion of the vortex and its interaction with the pressure surface are cyclic. The vortex breakdown causes significant changes in the nature of the tip leakage vortex, which result in the anomalous phenomena in the time-averaged flow fields near the tip 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 t … More he low-energy fluid accumulating on the pressure side, and large pressure fluctuation on the pressure side. As the flow rate is decreased, the movement of the tip leakage vortex due to its breakdown becomes so large that the leakage vortex interacts with the suction surface as well as the pressure one. The interaction with the suction surface gives rise to the three-dimensional separation of the suction surface boundary layer.Unsteady full passage flow fields at a near-stall operating condition in the axial compressor rotor has been investigated by RANS simulation. The simulation has captured the nature of the rotating stall inception. It is found that the stall cell is part-span type and consists of a tornado-type separation vortex linking from blade suction surface near the tip to the casing. The spiral-type breakdown of the tip leakage vortex causes the interaction between the leakage vortex and the adjacent blade leading edge, thus resulting in the formation of the tornado-type vortex. Less