Flow behaviors in a Kaplan turbine runner with different tip clearances

Yue Ma,Zongku Liu,Guangtai Shi,Xiaobing Liu,Xuan Wang,Bing Qian,Zhiguo Feng

doi:10.1177/16878140211015879

Abstract

Tip clearance between the runner blade tip and shroud in a Kaplan turbine is inevitable, and the tip leakage flow (TLF) and tip leakage vortex (TLV) induced by the tip clearance have a considerable effect on the flow behaviors. To reveal the effect of the tip clearance on the flow characteristics, based on the Reynolds time-averaged Navier-Stokes (N-S) equation and the shear stress transfer (SST) k-ω turbulence model, the three-dimensional turbulence flow in a Kaplan turbine is simulated using ANSYS CFX. Meanwhile, the flow laws in the tip clearance are emphatically analyzed and summarized. Results show with the increase of the tip clearance, the negative pressure region in the blade suction side (SS) middle, the SS near the blade tip and the blade tip becomes more and more obvious. In the meantime, the flow behaviors on the blade pressure side (PS) are relatively stable, and the flow separation on the SS near blade tip merges. The larger the tip clearance is, the more obvious the flow separation phenomenon displays. In addition, the TLV is a spatial three-dimensional spiral structure formed by the entrainment effect of the TLF and main flow, and as the tip clearance increases, the TLV becomes more obvious.

Highlights

As a core component of the global energy structure, hydropower has become the third largest energy source after coal and natural gas
Velocity on the blade suction side (SS) near the blade tip is larger, and as the tip clearance increases, flow separation occurs in the blade tip
The tip leakage flow (TLF) in the tip clearance is a necessary condition for the tip leakage vortex (TLV) formation, and the TLV is the inevitable result of the TLF development

Summary

Introduction

As a core component of the global energy structure, hydropower has become the third largest energy source after coal and natural gas. Guo et al.[17] adopt computational fluid dynamics (CFD) technology to investigate the effect of the clearance geometries on the flow field of a hydrofoil, and declared the sharp tip reduced the leakage flow losses and increased the velocity gradient. Based on the Zwart-Gerber-Belamri model cavitation model, Chen et al.[19] employed CFD method to unmask the effect of tip clearance on the cavitation flow in a Kaplan turbine. On account of the analysis above, the numerical simulation in present work is employed to investigate the effect of tip clearance on the inner flow characteristics in a Kaplan turbine runner, and the TFL and TLV characteristics are emphatically analyzed. Based on the Reynolds time-averaged N-S equation and Finite Volume Method (FVM), the ANSYS CFX is employed to simulate the three-dimensional flow in a Kaplan turbine runner with different tip clearances. The interface between rotational and stationary components is set to ‘‘Frozen Rotor,’’ and the interface between stationary components is set to ‘‘General Connection.’’ When the residual is lower than 1025 or the flow rate at outlet is stable, the simulation is considered convergence

Result and discussion

Conclusions