Investigation of tip leakage vortex characteristics around tip clearance in a mixed flow pump

Abstract

A systematical investigation on hydraulic performance and unsteady flow characteristics around tip clearance in a mixed-flow pump is conducted based on experimental results and steady simulation. The 1mm increase of tip clearance size results in that the pump head reduces by 1.79m, and pump efficiency decreases by 5.49% at design flow rate. At large flow rate, the performance drop remarkably increases compared with low flow rate and design flow rate. The unsteady simulation reveals the spatio-temporal evolution of TLV (tip leakage vortex), and interaction process of primary TLV and secondary TLV is also observed. The results show that at low and design flow rates, the start points of primary TLV are near leading edge, and the separation angle is always 25°. At large flow rate, the start point of primary TLV shifts towards trailing edge, and the separation angle decreases to 15°. Based on the statistical method, pressure fluctuations in tip clearance and on blade near leading edge are also analysed. The results show that strongest pressure fluctuations appear at regions near leading edge, and the flow instability is significantly intensified under low flow rate.