000139208 001__ 139208
000139208 005__ 20190812205329.0
000139208 037__ $$aCONF
000139208 269__ $$a2009
000139208 260__ $$c2009$$aBrno
000139208 336__ $$aConference Papers
000139208 520__ $$aAt part load operation of Francis turbine, the swirl in the draft tube leads to flow instability known as vortex breakdown. This flow instability can interact with the rest of the hydraulic circuit through axially propagating plane-waves. Moreover, at low cavitation index , the gaseous rope is suspected to modify locally the propagation velocity. Acoustic models have been commonly used to tackle this problematic. In order to validate the parameters of those models, an experiment with equivalent phenomenology has been setup. The experiment is designed so that the flow characteristic are similar to draft tube surge, but with strong simplification in order to facilitate the study of the flow instability and its interaction with the acoustic field. The hydraulic circuit consists in a square pipe connecting two constant pressure reservoirs. The excitation mechanism is obtained by the shedding of vortices in the wake of a bluff body placed at ¾ of the pipe length. The excitation frequency can be adjusted through the flow velocity. To examine the influence of vapor cavity formed in the wake of the obstacle, the mean pressure inside the pipe is also adjustable. Without cavitation, the analyses of the pressure field along the circuit highlights the acoustic modes shapes and Eigen frequencies of the system. It is also demonstrated that the amplitudes along the circuit are strongly increased as the excitation frequency matches the Eigen frequency of the system. In a second step, the relation of the cavitation index with the Eigen mode shapes and frequencies has been systematically analyzed. A direct influence of the vapor cavity on the local propagation velocity is shown. Finally, at particular cavitation index, important amplification of fluctuations has been noticed. From the author’s point of view, it is a consequence of the vapor volume unsteadiness.
000139208 6531_ $$ahydroacoustic
000139208 6531_ $$aresonnance
000139208 6531_ $$acavitation
000139208 700__ $$0243102$$g128646$$aRuchonnet, N.
000139208 700__ $$aNicolet, C.
000139208 700__ $$0243097$$g178059$$aAlligné, S.
000139208 700__ $$0241012$$g104417$$aAvellan, F.
000139208 7112_ $$dOctober 14-16, 2009$$cBrno$$a3rd IAHR International Meeting of the Workgroup on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems
000139208 720_1 $$aRudolf, Pavel$$eed.
000139208 773__ $$j2$$tProceedings of the 3rd IAHR International Meeting of the Workgroup on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems$$q501-514
000139208 8564_ $$zn/a$$uhttps://infoscience.epfl.ch/record/139208/files/paper%20IAHR%202009_final.pdf$$s735917
000139208 909C0 $$xU10309$$pLMH$$0252135
000139208 909CO $$ooai:infoscience.tind.io:139208$$qGLOBAL_SET$$pconf$$pSTI
000139208 917Z8 $$x128646
000139208 937__ $$aLMH-CONF-2009-002
000139208 973__ $$rNON-REVIEWED$$sPUBLISHED$$aEPFL
000139208 980__ $$aCONF