000205216 001__ 205216
000205216 005__ 20190812205825.0
000205216 02470 $$2ISI
000205216 0247_ $$a10.1088/1755-1315/22/3/032034$$2doi
000205216 02470 $$a000347441900092
000205216 037__ $$aCONF
000205216 245__ $$aOn the physical mechanisms governing self-excited pressure surge in Francis turbines
000205216 260__ $$c2014$$bIOP Publishing Ltd$$aBristol
000205216 269__ $$a2014
000205216 300__ $$a8
000205216 336__ $$aConference Papers
000205216 490__ $$aIOP Conference Series-Earth and Environmental Science$$v22
000205216 520__ $$aThe required operating range for hydraulic machines is continually extended in an effort to integrate renewable energy sources with unsteady power outputs into the existing electrical grid. The off-design operation however brings forth unfavorable flow patterns in the machine, causing dynamic problems involving cavitation, which may represent a limiting factor to the energy production. In Francis turbines it is observed that the self-excited oscillation of a vortex rope in the draft tube cone prevents the delivery of maximum power when required. This phenomenon is referred to as full load pressure surge and has been the object of extensive research during the past decades. Several contributions deepened its understanding through measurement and simulation of the local flow properties and the global stability parameters. The draft tube pressure level and the runner outlet swirl are identified as key variables in the modelling of the vortex rope dynamics. Recently, a cyclic appearance of blade cavitation has been observed at overload conditions in a multiphase numerical simulation coupling the runner and the draft tube. From the analysis of the simulation it becomes obvious that the cyclic appearance of blade cavitation has a direct effect on the runner outlet swirl, thus introducing an additional interaction mechanism that is not accounted for in formerly published models. For the presented work, the results of this numerical study are confirmed experimentally on a reduced scale model of a Francis turbine. Several wall pressure measurements in the draft tube cone are performed, together with high speed visualizations of the vortex rope and the blade cavitation. The flow swirl is calculated based on Laser Doppler Velocimetry measurements. A possible mechanism explaining the coupling between the self-excited pressure and vortex rope oscillation and the cyclic appearance of the blade cavitation is proposed. Furthermore, the streamwise propagation speed of the flow swirl in the draft tube is calculated. The results offer important insights in the physics of high load pressure surge and contribute to the further development of numerical draft tube flow and stability models.
000205216 542__ $$fCC BY
000205216 700__ $$aMüller, Andres$$0244116
000205216 700__ $$aFavrel, A.
000205216 700__ $$aLandry, C.
000205216 700__ $$aYamamoto, K.
000205216 700__ $$aAvellan, F.$$0241012$$g104417
000205216 7112_ $$dSeptember 22-26, 2014$$cMontréal, Québec, Canada$$a27th IAHR Symposium on Hydraulic Machinery and Systems (IAHR 2014)
000205216 7112_ $$dSeptember 22-26, 2014$$cMontréal, Canada$$a27th IAHR Symposium on Hydraulic Machinery and Systems
000205216 720_1 $$aDesy, N$$eed.
000205216 720_1 $$aDeschenes, C$$eed.
000205216 720_1 $$aGuibault, F$$eed.
000205216 720_1 $$aPage, M$$eed.
000205216 720_1 $$aTurgeon, M$$eed.
000205216 720_1 $$aGiroux, Am$$eed.
000205216 773__ $$j22$$t27th IAHR Symposium on Hydraulic Machinery and Systems (IAHR 2014)$$q1-8
000205216 8564_ $$uhttps://infoscience.epfl.ch/record/205216/files/On%20the%20physical%20mechanisms%20governing%20self-excited%20pressure%20surge%20in%20Francis%20turbines.pdf$$s2314593
000205216 8564_ $$xpdfa$$uhttps://infoscience.epfl.ch/record/205216/files/On%20the%20physical%20mechanisms%20governing%20self-excited%20pressure%20surge%20in%20Francis%20turbines.pdf?subformat=pdfa$$s3542973
000205216 8560_ $$femilie.reynaud@epfl.ch
000205216 909C0 $$xU10309$$pLMH$$0252135
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000205216 937__ $$aEPFL-CONF-205216
000205216 973__ $$rREVIEWED$$aEPFL
000205216 980__ $$aCONF