LES of Transients in the Francis-99 Turbine

Abstract

Most water turbines are designed to only operate at their best efficiency point and to hardly ever change their operation condition. Modern life and new energy sources pushes the demands making the hydro turbines work as stabilizers to the electric grid. Thus, varying its operation point several times a day. The majority of today’s water turbines have a confidential design, leading to difficulties for academia and companies to do research. Hence the creation of the Francis-99 workshops. It is an open access study containing both experimental data and a Francis turbine geometry. This thesis presents CFD simulations of transients, using LES in OpenFOAM, based on the Francis-99 design. An entire shutdown sequence and four short start-up scenarios are simulated and verified against available experimental data. The numerically simulated data matches the experimental to a great extent. Making the simulation strategy highly suitable to perform more comprehensive investigations e.g. to find optimal transients between operation points that reduce stresses on the turbine. It is further concluded that the axial torque varies linearly with the operation point and that the axial thrust is fairly constant. Also found is that the runner exhibits unwanted radial loads during shutdown which, with time, may fatigue the machine.