000139297 001__ 139297
000139297 005__ 20190601102525.0
000139297 0247_ $$2doi$$a10.1115/1.3155944
000139297 02470 $$2ISI$$a000268405500002
000139297 037__ $$aARTICLE
000139297 245__ $$aExperimental Evidence of Hydroacoustic Pressure Waves in a Francis Turbine Elbow Draft Tube for Low Discharge Conditions
000139297 269__ $$a2009
000139297 260__ $$c2009
000139297 336__ $$aJournal Articles
000139297 520__ $$aThe complex three-dimensional unsteady flow developing in the draft tube of a Francis turbine is responsible for pressure fluctuations, which could prevent the whole hydropower plant from operating safely. Indeed, the Francis draft tube is subjected to inlet swirling flow, divergent cross section, and the change of flow direction. As a result, in low discharge off-design operating conditions, a cavitation helical vortex, so-called the vortex rope develops in the draft tube and induces pressure fluctuations in the range of 0.2–0.4 times the runner frequency. This paper presents the extensive unsteady wall pressure measurements performed in the elbow draft tube of a high specific speed Francis turbine scale model at low discharge and at usual plant value of the Thoma cavitation number. The investigation is undertaken for operating conditions corresponding to low discharge, i.e., 0.65–0.85 times the design discharge, which exhibits pressure fluctuations at surprisingly high frequency value, between 2 and 4 times the runner rotation frequency. The pressure fluctuation measurements performed with 104 pressure transducers distributed on the draft tube wall, make apparent in the whole draft tube a fundamental frequency value at 2.5 times the runner frequency. Moreover, the modulations between this frequency with the vortex rope precession frequency are pointed out. The phase shift analysis performed for 2.5 times the runner frequency enables the identification of a pressure wave propagation phenomenon and indicates the location of the corresponding pressure fluctuation excitation source in the elbow; hydroacoustic waves propagate from this source both upstream and downstream the draft tube.
000139297 6531_ $$acavitation
000139297 6531_ $$aflow instability
000139297 6531_ $$aPoiseuille flow
000139297 6531_ $$apower plants
000139297 6531_ $$apressure transducers
000139297 6531_ $$aturbines
000139297 6531_ $$avortices
000139297 6531_ $$awaves
000139297 6531_ $$aVortex Breakdown Phenomenon
000139297 6531_ $$aFlow
000139297 700__ $$aArpe, Jorge
000139297 700__ $$aNicolet, Christophe
000139297 700__ $$0241012$$g104417$$aAvellan, François
000139297 773__ $$j131$$tJournal of Fluids Engineering$$q081102
000139297 8564_ $$zURL
000139297 8564_ $$uhttps://infoscience.epfl.ch/record/139297/files/JFE_proof_print.pdf$$zn/a$$s1560388
000139297 909C0 $$xU10309$$0252135$$pLMH
000139297 909CO $$ooai:infoscience.tind.io:139297$$qGLOBAL_SET$$pSTI$$particle
000139297 937__ $$aLMH-ARTICLE-2009-018
000139297 973__ $$rREVIEWED$$sPUBLISHED$$aEPFL
000139297 980__ $$aARTICLE