Effect of tip clearance flow on pressure oscillation and vortex patterns of a high-speed centrifugal pump

Abstract

In a micro centrifugal pump with tip clearance working at high speed, the pressure fluctuation and complex vortex structures related to the tip leakage flow are conducted. The external characteristics calculated by the numerical simulation and experiment method agree well, and the maximum deviation of the simulated pump head and efficiency compared with the experimental data is less than 5%. The vortex structures induced by the tip clearance flow, which is less influenced by the flow conditions, can be divided into four categories, namely backflow vortex, passage vortex, primary tip clearance flow (PTLV), and separation TLV (STLV). The evolution of these vortex structures is described by the relative vorticity transport equation, using the relative vortex stretching, Coriolis force, and viscous diffusion. The PTLV starts from the corner of blade tip gap near the leading edge (LE), and breaks away into the STLV in the region of 0.7 R* to 0.8 R* owing to the pushing effect of the secondary tip leakage flow. To analyze the leakage flow quantitatively, the relative velocity in the gap region is decomposed. The results show that the local maximal and minimal values of the normal component correspond to the start position of the PTLV and the separation region of the STLV, respectively. Besides, the passage vortex has the greatest contribution to the pressure pulsation of the passage from main blade to main blade (MB). But the dominant frequency of the pressure alterations has little to do with the vortex, and mainly depends on the rotor-stator interaction (RSI) between the impeller and volute tongue. The results could be referred to improve the efficiency and operational stability of the high-speed centrifugal pumps.