000032276 001__ 32276
000032276 005__ 20190509131920.0
000032276 0247_ $$2doi$$a10.5075/epfl-thesis-1799
000032276 02471 $$2nebis$$a1946400
000032276 037__ $$aTHESIS
000032276 041__ $$afre
000032276 088__ $$a1799
000032276 245__ $$aAnalyse et prédiction de la baisse de rendement des turbines Francis par cavitation à bulles
000032276 269__ $$a1998
000032276 260__ $$bEPFL$$c1998$$aLausanne
000032276 300__ $$a307
000032276 336__ $$aTheses
000032276 520__ $$aThe setting level of an hydraulic machine, specially for low head machines, is decided with respect to the possible alteration of the efficiency due to the cavity development. This alteration can easily be noticed by plotting the evolution of the efficiency η as a function of the Thoma number σ leading to the so-called η – σ cavitation curves. Observation of the cavity extent in the flow passage of the runner allows to associate the drop of efficiency with a particular type of cavity development. However, depending on the type of cavities this drop cannot be very easily explained. Obviously, for a leading edge attached cavity corresponding to high head operating points, the presence of the vapour phase on the blade suction side limits the pressure at the vapour pressure value which causes the flow alteration. In the case of travelling bubble cavitation, corresponding to the outlet cavitation at the nominal head, this limitation of the pressure field due to the presence of the vapour was never characterized. In order to protect the efficiency at the best operating point against the travelling bubbles effects, the IEC norms suggests some measures relating to turbines standards cavitation tests. These measures are based on the systematic control of the test water quality in term of nucleation, which is the main factor of the inception of this type of cavitation. A prediction method of the efficiency drop due to the outlet travelling bubble cavitation is then a necessity from the point of view of the possibility to modify the runner geometry in the first state of the project. The main object of this work is then the understanding of the physical phenomenon acting on the Francis turbine efficiency alteration with a development of travelling bubble cavitation in order to elaborate a prediction method. The first aspect of this thesis work is the characterisation of the bubbles influence with some experiments carried out in the hydraulic machines tests rigs and the high-speed cavitation tunnel. The second part consists in the development of a cavitating pressure field prediction method. The main work is finally intented to analyse the actual standards cavitation tests methods.
000032276 6531_ $$atravelling bubble cavitation
000032276 6531_ $$aFrancis turbine
000032276 6531_ $$aefficiency
000032276 6531_ $$astandards cavitation tests
000032276 6531_ $$aprediction
000032276 6531_ $$ahydraulic machines tests rig
000032276 6531_ $$acavitation tunnel
000032276 6531_ $$apressure measurements on a blade
000032276 6531_ $$ahigh-speed vizualisations
000032276 6531_ $$anumerical computation
000032276 6531_ $$acavitation à bulles
000032276 6531_ $$aturbine Francis
000032276 6531_ $$arendement
000032276 6531_ $$aessais standards
000032276 6531_ $$aprédiction
000032276 6531_ $$aplate-forme d'essai
000032276 6531_ $$atunnel de cavitation
000032276 6531_ $$amesures de pression sur une aube
000032276 6531_ $$avisualisations rapides
000032276 6531_ $$acalculs numériques
000032276 700__ $$aArn, Christophe
000032276 720_2 $$aAvellan, François$$edir.$$g104417$$0241012
000032276 8564_ $$uhttps://infoscience.epfl.ch/record/32276/files/EPFL_TH1799.pdf$$zTexte intégral / Full text$$s11353582$$yTexte intégral / Full text
000032276 909C0 $$xU10309$$0252135$$pLMH
000032276 909CO $$pSTI$$pDOI$$ooai:infoscience.tind.io:32276$$qDOI2$$qGLOBAL_SET$$pthesis
000032276 919__ $$aLMH
000032276 920__ $$b1998
000032276 970__ $$a1799/THESES
000032276 973__ $$sPUBLISHED$$aEPFL
000032276 980__ $$aTHESIS