Study on flow instability and countermeasure in a draft tube with swirling flow

Takahiro Nakashima, Ryo Matsuzaka, Kazuyoshi Miyagawa, Koichi Yonezawa, Yoshinobu Tsujimoto

    Research output: Contribution to journalArticle

    4 Citations (Scopus)

    Abstract

    The swirling flow in the draft tube of a Francis turbine can cause the flow instability and the cavitation surge and has a larger influence on hydraulic power operating system. In this paper, the cavitating flow with swirling flow in the diffuser was studied by the draft tube component experiment, the model Francis turbine experiment and the numerical simulation. In the component experiment, several types of fluctuations were observed, including the cavitation surge and the vortex rope behaviour by the swirling flow. While the cavitation surge and the vortex rope behaviour were suppressed by the aeration into the diffuser, the loss coefficient in the diffuser increased by the aeration. In the model turbine test the aeration decreased the efficiency of the model turbine by several percent. In the numerical simulation, the cavitating flow was studied using Scale-Adaptive Simulation (SAS) with particular emphasis on understanding the unsteady characteristics of the vortex rope structure. The generation and evolution of the vortex rope structures have been investigated throughout the diffuser using the iso-surface of vapor volume fraction. The pressure fluctuation in the diffuser by numerical simulation confirmed the cavitation surge observed in the experiment. Finally, this pressure fluctuation of the cavitation surge was examined and interpreted by CFD.

    Original languageEnglish
    Article numberA02
    Pages (from-to)230-239
    Number of pages10
    JournalInternational Journal of Fluid Machinery and Systems
    Volume8
    Issue number4
    DOIs
    Publication statusPublished - 2015

    Keywords

    • Aeration
    • Cavitation
    • Draft tube
    • Hydro turbine
    • Vortrex rope

    ASJC Scopus subject areas

    • Industrial and Manufacturing Engineering
    • Mechanical Engineering

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