000228897 001__ 228897
000228897 005__ 20190917061310.0
000228897 0247_ $$2doi$$a10.5075/epfl-thesis-7730
000228897 02470 $$2urn$$aurn:nbn:ch:bel-epfl-thesis7730-2
000228897 02471 $$2nebis$$a10912627
000228897 037__ $$aTHESIS
000228897 041__ $$aeng
000228897 088__ $$a7730
000228897 245__ $$aHydrodynamics of Francis turbine operation at deep part load condition
000228897 260__ $$bEPFL$$c2017$$aLausanne
000228897 269__ $$a2017
000228897 300__ $$a175
000228897 336__ $$aTheses
000228897 502__ $$aProf. Jürg Alexander Schiffmann (président) ; Prof. François Avellan (directeur de thèse) ; Prof. Karen Mulleners, Dr Alexander Jung, Prof. Kazuyoshi Miyagawa (rapporteurs)
000228897 520__ $$aThe electrical energy production from New and Renewable Energy (NRE) sources have become increasingly important in the past decades. However, intermittent electrical generation from NRE sources due to their stochastic nature often prevents stable power output from existing power grids. To enable a smooth integration of NRE sources, flexible operations at hydraulic power plants are key to providing the capability of primary and secondary grid control to balance the energy production. The rapid growth of the NRE sources nonetheless requires hydraulic machines to function in an extended operating range, especially down to extremely low discharge conditions called deep part load operation. Such off-design conditions provoke various types of cavitation flows, posing a threat to stable operations at hydraulic units. Inter-blade cavitation vortices are a typical example of cavitation phenomena observed at deep part load operation. However, its dynamic characteristics are insufficiently understood today. The main objective of the present research is to unveil the flow characteristics at deep part load conditions and the physical mechanisms responsible for the inter-blade vortex development. The experimental is carried out with a physical reduced scale model of a Francis turbine. The characteristics of the flow in the draft tube is first investigated by wall pressure fluctuation and velocity surveys by PIV (Particle Image Velocimetry) measurements. For investigations of inter-blade cavitation vortices, the present study introduces a novel visualization technique using an instrumented guide vane, providing unprecedented images of cavitation development inside the runner blade channel. The binary image processing technique enables the successful evaluation of inter-blade cavitation vortices in the images. The analyses demonstrate that the probability of the inter-blade cavitation development is significantly high close to the runner hub. Furthermore, the mean vortex line is calculated. Additionally, the impact of the inter-blade vortex on the pressure field is investigated by on-board instrumentation on the runner blade. It reveals that the presence of an inter-blade vortex induces stochastic pressure oscillations on the blade. Moreover, the survey of the wall pressure difference between pressure and suction sides of the blade suggests the development of a backflow region near the hub, which is closely related to inter-blade vortex development. In an effort to better understand the flow structure in the draft tube and inside the blade channel, numerical simulations by an unsteady RANS approach are performed. Flow analysis in the draft tube and the simulated inter-blade vortices are in good agreement with the experimental results. Furthermore, the simulated flow inside the blade channel confirms the development of a backflow region on the hub near the runner outlet. The skin-friction analyses evidence that the backflow region as well as inter-blade vortex development are provoked by flow separation on the hub, which is caused by the misaligned flow condition inside the blade channel. The investigations are furthermore extended to identify the influence of inter-blade vortices on the specific energy dissipation in the runner. The quantitative evolution of the specific energy loss using the specific rothalpy reveals that inter-blade vortices cause the energy loss through the blade channel.
000228897 6531_ $$aFrancis turbine
000228897 6531_ $$adeep part load
000228897 6531_ $$acavitation
000228897 6531_ $$ainter-blade vortex
000228897 6531_ $$avisualization
000228897 6531_ $$aon-board measurement
000228897 6531_ $$anumerical simulation
000228897 6531_ $$aunsteady RANS
000228897 700__ $$0247344$$g230846$$aYamamoto, Keita
000228897 720_2 $$aAvellan, François$$edir.$$g104417$$0241012
000228897 8564_ $$zn/a$$yn/a$$uhttps://infoscience.epfl.ch/record/228897/files/EPFL_TH7730.pdf$$s59197104
000228897 909C0 $$xU10309$$0252135$$pLMH
000228897 909CO $$pthesis$$pthesis-bn2018$$pDOI$$ooai:infoscience.tind.io:228897$$qDOI2$$qGLOBAL_SET$$pSTI
000228897 917Z8 $$x108898
000228897 917Z8 $$x252028
000228897 918__ $$dEDEY$$cIGM$$aSTI
000228897 919__ $$aLMH
000228897 920__ $$b2017$$a2017-6-16
000228897 970__ $$a7730/THESES
000228897 973__ $$sPUBLISHED$$aEPFL
000228897 980__ $$aTHESIS