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research-article

Spatial-temporal evolution of tip leakage vortex in a mixed flow pump with tip clearance

[+] Author and Article Information
Yabin Liu

State Key Laboratory of Hydroscience and Engineering, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
liuyabin_thu@163.com

Lei Tan

State Key Laboratory of Hydroscience and Engineering, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
tanlei@mail.tsinghua.edu.cn

1Corresponding author.

ASME doi:10.1115/1.4042756 History: Received September 04, 2018; Revised January 28, 2019

Abstract

Tip clearance in pump induces tip leakage vortex (TLV), which interacts with the main flow and leads to instability of flow pattern and drop of energy performance. In the present work, the characteristics of TLV in a mixed flow pump are investigated by the numerical simulation using SST k-? turbulence model with experimental validation. The trajectory of primary tip leakage vortex (PTLV) is labeled out, and a power function law is proposed to describe the intensity of PTLV core along the trajectory. Spatial-temporal evolution of TLV in an impeller revolution can be classified into three stages: splitting stage, developing stage and merging stage. The TLV oscillation period TT is found as 19/160 T, corresponding to the frequency 8.4 fi (fi is impeller rotating frequency). Results reveal that the TLV oscillation is induced by the sudden pressure variation at the junction of two adjacent blades. On analysis of the relative vorticity transport equation, it is revealed that the relative vortex stretching item in Z direction is the major source of the splitting and shedding of PTLV. The dominant frequency of pressure and vorticity fluctuations in PLTV trajectory is 8.4 fi, which is the same as the TLV oscillation frequency. This result reveals that the flow instability in PLTV trajectory is dominated by the oscillation of TLV. The blade number has significant effect on pressure fluctuation in tip clearance and on blade pressure side, because the TLV oscillation period varies with the circumferential length of flow passage.

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