Abstract
The tip gap existing between the blade tip and casing can give rise to tip leakage flow and interfere with the main flow, which causes unstable flow characteristics and intricate vortex in the passage. Investigation on the tip clearance effect is of great important due to its extensive applications in the rotating component of pumps. In this study, a scaling axial flow pump used in a south-north water diversion project with different sizes of tip clearances was employed to study the tip clearance effect on tip leakage vortex (TLV) characteristics. This analysis is based on a modified turbulence model. Validations were carried out using a high-speed photography technique. The tip clearance effect on the generation and evolution of TLV was investigated through the mean velocity, pressure, and vorticity fields. Results show that there are two kinds of TLV structures in the tip region. Accompanied by tip clearance increasing, the viscous loss in the tip area of the axial flow pump increases. Furthermore, the tip clearance effect on pressure distribution in the blade passage is discussed. Beyond that, the tip clearance effect on vortex core pressure and cavitation is studied.
Highlights
In the past decades, the speedy development of hydraulic power plants [1] and water pump factories [2] has greatly stimulated research investigating different kinds of flow pumps worldwide
To validate the simulation method, the parameters set in the simulations were kept consistent with that in the experiments
Large eddy simulation was employed to predict the external performance under different flow rates
Summary
The speedy development of hydraulic power plants [1] and water pump factories [2] has greatly stimulated research investigating different kinds of flow pumps worldwide. Comprehensive studies have investigated the effect of tip gap sizes on the operating performance and flow characteristics in rotating machinery. Tan et al [11,12] studied the operating performance and flow patterns of mixed flow pumps with different tip gap sizes experimentally and numerically. The TLV is usually accompanied by tip clearance cavitation and shear layer cavitation These complex cavitation interfere with each other, reduce the blade load, and induce flow instability. The tip leakage flows and related cavitation in the tip region of an axial flow pump were investigated experimentally and numerically by Shi et al [28,29]. The effects of different tip clearances on the TLV characteristics of an axial flow pump were investigated systematically.
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