Numerical study of instability mechanism in the air-core vortex formation process

Kan Kan, Yuhang Xu, Zhixiang Li, Hui Xu, Huixiang Chen, Dan Zi, Qiang Gao, Lian Shen

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

Air-core vortices are a ubiquitous phenomenon in the intakes of hydropower stations. Due to the transient and instability of two-phase vorticial flow, the prediction of air-core vortex formation is challenging, and understanding of the instability mechanism remains elusive. In this study, the large eddy simulation (LES) method and a coupled level-set and volume-of-fluid (CLSVOF) method are performed to study air-core vortex formation in a benchmark reservoir with a horizontal intake pipe. The process of air-core vortex formation can be classified into an inception stage, an instability stage, and a stability stage. In the instability stage, the surface vortex repeatedly goes through the process of inception, enhancement, attenuation, and extinction. The movement of the counterrotating secondary vortices and water surface level fluctuation plays a negative role in air-core vortex formation. The additional motion generated by the counterrotating pair drives the pair to the back wall. The main vortex undergoes attenuation due to the stretching/tilting effects induced by the secondary vortex. Water level fluctuations briefly increase the submergence depth, which in turn reduces the vertical velocity gradient and vertical vorticity, destabilizing the vortex. The perturbation of the air-core vortex by water level fluctuations is present only at the beginning of the instability stage.

Original languageEnglish (US)
Article number2156926
JournalEngineering Applications of Computational Fluid Mechanics
Volume17
Issue number1
DOIs
StatePublished - 2023

Bibliographical note

Funding Information:
This work was supported by National Natural Science Foundation of China [grant number 52006053,52009033]; Natural Science Foundation of Jiangsu Province [grant number BK20200508,BK20200509]; Postdoctoral Research Foundation of China [grant number 2022T150185,2021M690876,2022M711021].

Publisher Copyright:
© 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.

Keywords

  • Air-core vortex
  • counterrotating pair
  • large eddy simulation
  • water level fluctuation
  • wave

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