000255329 001__ 255329
000255329 005__ 20190317000955.0
000255329 037__ $$aCONF
000255329 245__ $$aAxisymmetric swirling flow simulation of the draft tube vortex in Francis turbines at partial discharge
000255329 260__ $$bInternational Association For Hydraulic Research$$c2008
000255329 269__ $$a2008
000255329 300__ $$a10
000255329 336__ $$aConference Papers
000255329 520__ $$aThe 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 in commercial codes for the Reynolds Averaged Navier-Stokes (RANS) equations in cylindrical coordinates with vanishing circumferential derivatives. Second, we modify the above solver 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 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 extending the operating range for Francis turbines.
000255329 542__ $$fCC BY
000255329 6531_ $$adraft tube, vortex rope, turbulent axisymmetric flow, stagnant region model
000255329 700__ $$aSusan-Resigna, Romeo
000255329 700__ $$aMuntean, Sebastian
000255329 700__ $$aStein, Peter
000255329 700__ $$0241012$$aAvellan, François
000255329 7112_ $$a24th Symposium on Hydraulic Machinery and Systems$$cFoz do Iguassu, Brazil$$dOctober 27-31, 2008
000255329 773__ $$j1$$q1-10$$tProceedings of the 24th Symposium on Hydraulic Machinery and Systems
000255329 8560_ $$femilie.reynaud@epfl.ch
000255329 8564_ $$s1551470$$uhttps://infoscience.epfl.ch/record/255329/files/Axisymmetric%20swirling%20flow%20simulation%20of%20the%20draft%20tube%20vortex%20in%20Francis%20turbines%20at%20partial%20discharge.pdf
000255329 8564_ $$s2931212$$uhttps://infoscience.epfl.ch/record/255329/files/Axisymmetric%20swirling%20flow%20simulation%20of%20the%20draft%20tube%20vortex%20in%20Francis%20turbines%20at%20partial%20discharge.pdf?subformat=pdfa$$xpdfa
000255329 909C0 $$0252135$$mfrancois.avellan@epfl.ch$$pLMH$$xU10309
000255329 909CO $$ooai:infoscience.epfl.ch:255329$$pconf$$pSTI$$qGLOBAL_SET
000255329 960__ $$aemilie.reynaud@epfl.ch
000255329 961__ $$alaurence.gauvin@epfl.ch
000255329 973__ $$aEPFL$$rREVIEWED
000255329 980__ $$aCONF
000255329 981__ $$aoverwrite