International Journal of Fluid Machinery and Systems

한국유체기계학회 (Korean Society for Fluid machinery)
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Axisymmetric Swirling Flow Simulation of the Draft Tube Vortex in Francis Turbines at Partial Discharge

  • Susan-Resiga, Romeo (Department of Hydraulic Machinery, "Politehnica" University of Timisoara) ;
  • Muntean, Sebastian (Center for Advanced Research in Engineering Science, Romanian Academy - Timisoara Branch) ;
  • Stein, Peter (VA TECH HYDRO) ;
  • Avellan, Francois (Laboratory for Hydraulic Machines, Ecole Polytechnique Federale de Lausanne)
  • 심사 : 2009.09.20
  • 발행 : 2009.12.01
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초록

The flow in the draft tube cone of Francis turbines operated at partial discharge is a complex hydrodynamic phenomenon where an incoming steady axisymmetric swirling flow evolves into a three-dimensional unsteady flow field with precessing helical vortex (also called vortex rope) and associated pressure fluctuations. The paper addresses the following fundamental question: is it possible to compute the circumferentially averaged flow field induced by the precessing vortex rope by using an axisymmetric turbulent swirling flow model? In other words, instead of averaging the measured or computed 3D velocity and pressure fields we would like to solve directly the circumferentially averaged governing equations. As a result, one could use a 2D axi-symmetric model instead of the full 3D flow simulation, with huge savings in both computing time and resources. In order to answer this question we first compute the axisymmetric turbulent swirling flow using available solvers by introducing a stagnant region model (SRM), essentially enforcing a unidirectional circumferentially averaged meridian flow as suggested by the experimental data. Numerical results obtained with both models are compared against measured axial and circumferential velocity profiles, as well as for the vortex rope location. Although the circumferentially averaged flow field cannot capture the unsteadiness of the 3D flow, it can be reliably used for further stability analysis, as well as for assessing and optimizing various techniques to stabilize the swirling flow. In particular, the methodology presented and validated in this paper is particularly useful in optimizing the blade design in order to reduce the stagnant region extent, thus mitigating the vortex rope and expending the operating range for Francis turbines.

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참고문헌

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피인용 문헌

  1. Analysis and Prevention of Vortex Breakdown in the Simplified Discharge Cone of a Francis Turbine vol.132, pp.5, 2010, https://doi.org/10.1115/1.4001486
  2. Unsteady Pressure Analysis of a Swirling Flow With Vortex Rope and Axial Water Injection in a Discharge Cone vol.134, pp.8, 2012, https://doi.org/10.1115/1.4007074
  3. An Outlook on the Draft-Tube-Surge Study vol.6, pp.1, 2013, https://doi.org/10.5293/IJFMS.2013.6.1.033
  4. Swirling and cavitating flow suppression in a cryogenic liquid turbine expander through geometric optimization vol.229, pp.6, 2015, https://doi.org/10.1177/0957650915589062
  5. Modelling and optimization of the velocity profiles at the draft tube inlet of a Francis turbine within an operating range vol.54, pp.1, 2016, https://doi.org/10.1080/00221686.2015.1119763
  6. Computational and Theoretical Analyses of the Precessing Vortex Rope in a Simplified Draft Tube of a Scaled Model of a Francis Turbine vol.139, pp.2, 2017, https://doi.org/10.1115/1.4034693