Numerical investigation of the air injection effect on the cavitating flow in Francis hydro turbine

D. V. Chirkov, P. K. Shcherbakov, S. G. Cherny, V. A. Skorospelov, P. A. Turuk

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)

Abstract

At full and over load operating points, some Francis turbines experience strong self-excited pressure and power oscillations. These oscillations are occuring due to the hydrodynamic instability of the cavitating fluid flow. In many cases, the amplitude of such pulsations may be reduced substantially during the turbine operation by the air injection/ admission below the runner. Such an effect is investigated numerically in the present work. To this end, the hybrid one-three-dimensional model of the flow of the mixture “liquid−vapor” in the duct of a hydroelectric power station, which was proposed previously by the present authors, is augmented by the second gaseous component — the noncondensable air. The boundary conditions and the numerical method for solving the equations of the model are described. To check the accuracy of computing the interface “liquid−gas”, the numerical method was applied at first for solving the dam break problem. The algorithm was then used for modeling the flow in a hydraulic turbine with air injection below the runner. It is shown that with increasing flow rate of the injected air, the amplitude of pressure pulsations decreases. The mechanism of the flow structure alteration in the draft tube cone has been elucidated, which leads to flow stabilization at air injection.

Original languageEnglish
Pages (from-to)691-703
Number of pages13
JournalThermophysics and Aeromechanics
Volume24
Issue number5
DOIs
Publication statusPublished - 1 Sep 2017

Keywords

  • air injection
  • cavitation
  • hydro turbines
  • numerical modeling
  • self-excited oscillations

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