Pressure fluctuation and flow pattern of a mixed-flow pump with different blade tip clearances under cavitation condition

Yun Xu,Shuliang Cao,Lei Tan,Yabin Liu

doi:10.1177/1687814017696227

Abstract

Cavitation phenomenon has strong transient characteristics and is highly influenced by geometric structure. In this study, the cavitation performance with influence of blade tip clearance for a mixed-flow pump is studied using the renormalization group (RNG) k–ε turbulence model and the Zwart–Gerber–Belamri cavitation model. The dominant frequency and maximum amplitude values at non-cavitation condition and different cavitation conditions are compared and associated with flow field features. The results show that the dominant frequency value under incipient cavitation and critical cavitation is 3.2 fi and when the cavitation is severe, the frequency value changes to 3.5 fi. Then, the influence of tip clearance width on cavitation performance of the mixed-flow pump is also discussed. The results show that the increase in tip clearance will significantly aggravate the performance drop of the pump under cavitation conditions. The critical net positive suction head value increases in 4.79% of the value under no-tip clearance condition. At the same time, by the inner flow field observation and analysis, the morphological of cavitation bubbles is also changed, and the cavitation bubbles tend to attach to the blade suction side and the attachment length increases as the tip clearance increases.

Highlights

Cavitation is a common hydrodynamic phenomenon in all kinds of hydraulic machineries
The transient characteristics under different cavitation conditions and the influence of blade tip clearance on the cavitation performance of a mixed-flow pump have been investigated, and the main conclusions can be drawn as follows: 1. For non-cavitation condition, the dominant frequencies are the multiples of the rotation frequency, while for cavitation condition, the dominant fluctuation becomes different
The incipient cavitation and critical cavitation conditions have the same dominant frequency of 3.2fi, while the severe cavitation condition has the dominant frequency of 3.5fi

Summary

Introduction

Cavitation is a common hydrodynamic phenomenon in all kinds of hydraulic machineries. Many researches have been performed on the cavitation performance of pumps in many aspects using different methods.[1,2,3,4,5,6] Due to the complicated distribution and variation of the multiphase flow in the cavitating pump, the transient characteristics of cavitation phenomenon should be investigated. Most existing papers of mixed-flow pump cavitation performance are studied. The mixed-flow pump has geometric similarities with axial flow pumps and inducers especially at impeller region, so the tip clearance should be concerned and studied. The transient characteristics of a mixedflow pump and the influence of tip clearance on the cavitation performance are investigated. The design of the pump impeller is based on direct inverse design method.[12,13,14] The model and meshes of the pump are shown in Figures 1 and 2, respectively

Computational methodology

Findings

Conclusion