000216525 001__ 216525
000216525 005__ 20181203024153.0
000216525 0247_ $$2doi$$a10.1007/s00348-015-2085-5
000216525 022__ $$a0723-4864
000216525 02470 $$2ISI$$a000366639800008
000216525 037__ $$aARTICLE
000216525 245__ $$aStudy of the vortex-induced pressure excitation source in a Francis turbine draft tube by particle image velocimetry
000216525 260__ $$bSpringer Verlag$$c2015$$aNew York
000216525 269__ $$a2015
000216525 300__ $$a15
000216525 336__ $$aJournal Articles
000216525 520__ $$achanges and loses its coherence, leading to a drastic reduction in the intensity of the induced excitation source. Francis turbines operating at part-load experience the development of a precessing cavitation vortex rope at the runner outlet, which acts as an excitation source for the hydraulic system. In case of resonance, the resulting pressure pulsations seriously compromise the stability of the machine and of the electrical grid to which it is connected. As such off-design conditions are increasingly required for the integration of unsteady renewable energy sources into the existing power system, an accurate assessment of the hydropower plant stability is crucial. However, the physical mechanisms driving this excitation source remain largely unclear. It is for instance essential to establish the link between the draft tube flow characteristics and the intensity of the excitation source. In this study, a two-component particle image velocimetry system is used to investigate the flow field at the runner outlet of a reduced-scale physical model of a Francis turbine. The discharge value is varied from 55 to 81 % of the value at the best efficiency point. A particular set-up is designed to guarantee a proper optical access across the complex geometry of the draft tube elbow. Based on phase-averaged velocity fields, the evolution of the vortex parameters with the discharge, such as the trajectory and the circulation, is determined for the first time. It is shown that the rise in the excitation source intensity is induced by an enlargement of the vortex trajectory and a simultaneous increase in the precession frequency, as well as the vortex circulation. Below a certain value of discharge, the structure of the vortex abruptly
000216525 700__ $$aFavrel, A.
000216525 700__ $$aMueller, A.
000216525 700__ $$aLandry, C.
000216525 700__ $$aYamamoto, K.
000216525 700__ $$g104417$$aAvellan, F.$$0241012
000216525 773__ $$j56$$tExperiments in Fluids$$k12$$q215
000216525 909C0 $$xU10309$$0252135$$pLMH
000216525 909CO $$pSTI$$particle$$ooai:infoscience.tind.io:216525
000216525 917Z8 $$x104417
000216525 917Z8 $$x253578
000216525 917Z8 $$x104417
000216525 937__ $$aEPFL-ARTICLE-216525
000216525 973__ $$rREVIEWED$$sPUBLISHED$$aEPFL
000216525 980__ $$aARTICLE