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Numerical analysis of unsteady flow under high‐head operating conditions in Francis turbine

Xiao Yexiang (State Key Laboratory of Hydroscience and Engineering & Department of Thermal Engineering, Tsinghua University, Beijing, China)
Wang Zhengwei (State Key Laboratory of Hydroscience and Engineering & Department of Thermal Engineering, Tsinghua University, Beijing, China)
Yan Zongguo (State Key Laboratory of Hydroscience and Engineering & Department of Thermal Engineering, Tsinghua University, Beijing, China)
Li Mingan (Yellow River Water & Hydropower Development Corporation, Jiyan city, China)
Xiao Ming (Yellow River Water & Hydropower Development Corporation, Jiyan city, China)
Liu Dingyou (Yellow River Water & Hydropower Development Corporation, Jiyan city, China)

Engineering Computations

ISSN: 0264-4401

Article publication date: 6 April 2010

929

Abstract

Purpose

The purpose of this paper is to describe how the hydraulic performance and pressure fluctuations in the entire flow passage of a Francis turbine were predicted numerically for the highest head. The calculations are used to partition the turbine operating regions and to clarify the unsteady flow behavior in the entire flow passage including the blade channel vortex in the runner and vortex rope in the draft tube.

Design/methodology/approach

Three‐dimensional unsteady numerical simulations were performed for a number of operating conditions at the highest head. The unsteady Reynolds‐averaged Navier‐Stokes equations with the kω based SST turbulence model were solved to model the unsteady flow within the entire flow passage of a Francis turbine.

Findings

The predicted pressure fluctuations in the draft tube agree well with the experimental results at low heads. However the peak‐to‐peak amplitudes in the spiral case are not as well predicted so the calculation domain and the inlet boundary conditions need to be improved. The unsteady simulation results are better than the steady‐state results. At the most unstable operating condition of case a0.5h1.26, the pulse in the flow passage is due to the rotor‐stator interference between the runner and the guide vanes, the blade channel vortex in the runner blade passage and the vortex rope in the draft tube.

Originality/value

This study investigates the characteristics of the dominant unsteady flow frequencies in different parts of the turbine for various guide vane openings at the highest head. The unsteady flow patterns in the turbine, including the blade channel vortex in the runner and the helical vortex rope in the draft tube, are classified numerically, and the turbine operating regions are partitioned to identify safe operating regions.

Keywords

Citation

Yexiang, X., Zhengwei, W., Zongguo, Y., Mingan, L., Ming, X. and Dingyou, L. (2010), "Numerical analysis of unsteady flow under high‐head operating conditions in Francis turbine", Engineering Computations, Vol. 27 No. 3, pp. 365-386. https://doi.org/10.1108/02644401011029934

Publisher

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Emerald Group Publishing Limited

Copyright © 2010, Emerald Group Publishing Limited

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