The swirling flow exiting the runner of a hydraulic turbine is further decelerated in the discharge cone of the draft tube to convert the excess of dynamic pressure into static pressure. When the turbine is operated far from the best efficiency regime, particularly at part load, the decelerated swirling flow develops a self-induced instability with a precessing helical vortex and the associated severe pressure fluctuations. This phenomenon is investigated numerically in this paper, for a swirl apparatus configuration. The unsteady three-dimensional (3D) flow field is analyzed using a proper orthogonal decomposition (POD), and within this framework we examine the effectiveness of an axial jet injection for mitigating the flow instability. It is shown that a limited number of modes can be used to reconstruct the flow field. Moreover, POD enables to reveal influence of the jet injection on the individual modes of the flow and illustrates continuous suppression of the modes from higher-order modes to lower-order modes as the jet discharge increases. Application of POD offers new view for the future control effort aimed on vortex rope mitigation because spatiotemporal description of the flow is provided. Thereby, POD enables better focus of the jets or other flow control devices.
Proper Orthogonal Decomposition of Self-Induced Instabilities in Decelerated Swirling Flows and Their Mitigation Through Axial Water Injection
Kaplan Department of Fluids Engineering,
Faculty of Mechanical Engineering,
Brno University of Technology,
Brno CZ-61669, Czech Republic
Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received June 20, 2016; final manuscript received February 17, 2017; published online May 17, 2017. Assoc. Editor: Oleg Schilling.
- Views Icon Views
- Share Icon Share
- Cite Icon Cite
- Search Site
Štefan, D., Rudolf, P., Muntean, S., and Susan-Resiga, R. (May 17, 2017). "Proper Orthogonal Decomposition of Self-Induced Instabilities in Decelerated Swirling Flows and Their Mitigation Through Axial Water Injection." ASME. J. Fluids Eng. August 2017; 139(8): 081101. https://doi.org/10.1115/1.4036244
Download citation file:
- Ris (Zotero)
- Reference Manager