Preliminary numerical simulations of a medium head Francis turbine at speed no-load

Authors: Gagnon, Pierre-Luc
Advisor: Houde, Sébastien
Abstract: This thesis presents the preliminary characterization of the flow in a medium head Francis turbine at speed no-load within the scope of the Tr-Francis project at the Hydraulic Machinery. Laboratory. Concretely, the project aims at validating the numerical methodology used with preliminary experimental measurements. Moreover, the numerical simulations will provide the fluid load for the FEA simulations. Ultimately, the results will allow identifying the dominant structures in the flow causing important fluctuations. Thus helping the experimental team to find the optimal location for the pressure sensors and the measuring planes. To do so, the numerical methodology is based on the measurements interpolation performed by Hydro-Québec on the prototype turbine at speed no-load. The data are applied, as they are, as the initial conditions for the prototype scale simulations. For the model scale simulations, they are scaled down using the similitude laws from the IEC 60193 standard. The effects of the inlet conditions are studied on partial domains with different mesh densities as well as on the complete domain. To validate the simulations, the pressure measurements obtained numerically in the draft tube are compared with the preliminary measurements and the results are in good agreement. Furthermore, the trailing edge cavitation observed numerically is also visible in experimental flow visualizations. Spectral analyses of pressure signals are used to help to characterize the phenomena. Different numerical visualization techniques are also used to isolate and analyse the main flow structures. Imposing a uniform velocity profile compared to the one obtained from the penstock and spiral case simulation does not significantly affect the results at model scale with the finest grid. Many important phenomena such as modulated inter-blades vortices, an important backflow region in the draft tube coming up to the runner, vortices generated in the draft tube in the shear layer, static pressure imbalance in the draft tube caused by the elbow and trailing blade cavitation were observed on the complete domain model scale simulations.
Document Type: Mémoire de maîtrise
Issue Date: 2021
Open Access Date: 15 November 2021
Grantor: Université Laval
Collection:Thèses et mémoires

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