Review of Kelvin-Helmholtz Instability and Vortex Breakdown in Tip Leakage Vortex
With the rapid development of renewable energy, pumped storage power plants have taken on critical functions such as frequency regulation and grid stabilization. Consequently, higher demands are placed on their core component—the pump-turbine—requiring further improvements in efficiency, extended service life, and reduced cavitation to ensure reliable and stable operation. Tip leakage flow (TLF) is a complex three-dimensional flow structure in pump turbines, as well as in other turbomachinery. In particular, it generates tip leakage vortex (TLV), which leads to severe damage of pump turbines in pumped storage power plants, such as dramatic efficiency decreases. It originates from the clearance between the blade tip and the casing. The pressure difference between the two sides of the blade drives fluid from the pressure side through the tip gap into the suction side. The process produces a distinct shear layer, leakage jet, and secondary vortex structures. In turbomachinery, performance degradation and structural failure often arise from unsteady flow features. One critical case is vortex breakdown (VB) caused by the TLV. This paper reviews unsteady mechanisms linked to vortex breakdown, including Kelvin-Helmholtz (KH) instability, cavitation, and, finally, the paper discusses geometric modulation to improve system efficiency and reduce cavitation. These factors act both as signals and as triggers of instability. KH structures, vortex breakdown, and cavitation modes together define the instability of tip leakage flows. Geometric and boundary conditions serve as tuning knobs for system sensitivity.