Numerical Investigations of Turbulent Flow in Water Turbines

This thesis investigates turbulent flow in water turbines, focusing onthe flow in the vicinity of reaction water turbine runners such as theKaplan runner and the Francis runner. The method of investigationis principally numerical although some experimental observations andmeasurements made in the present work and elsewhere are included.A major part of the present work was to implement an efficient andgeneral CFD (Computational Fluid Dynamics) code that could resolvethe complicated geometry of a water turbine. A parallel multiblockfinite volume CFD code, CALC-PMB (Parallel MultiBlock), was developed.The main features of the code are the use of conformal blockstructured boundary fitted coordinates, a pressure correction scheme(SIMPLEC), Cartesian velocity components as the principal unknownsand a collocated grid arrangement together with Rhie and Chow interpolation.The turbulence is modeled using a low-Reynolds k-omega turbulencemodel. The parallel multiblock algorithm employs two ghost cellplanes at the block interfaces. The message passing at the interfacesis done using either PVM (Parallel Virtual Machine) or MPI (MessagePassing Interface).Three water turbine runners are used for the investigations, two Kaplanrunners and one Francis runner. One of the Kaplan runners wasused during the development of the CFD code. This runner could notbe used to validate the CFD code but the work on this runner still gavevaluable insights on CFD in water turbines. The other Kaplan runneris a model of the runners installed in the H\ua8olleforsen power plant inIndals\ua8alven in Sweden. The computational results of the H\ua8olleforsenwicket gate and runner flow are validated against the thorough experimentalinvestigations from the Turbine 99 workshops and additionalLDV (Laser Doppler Velocimetry) measurements made in the presentwork. The Francis runner model investigated here was used as a testcase at a GAMM workshop in 1989. The present computational results of the GAMM Francis runner are validated against measurements atboth the best efficiency operating condition and four off-design operatingconditions. Several important flow features are visualized to makecomparisons with experimental observations and to better understandthe flow in water turbine runners. The validations against both detailedmeasurements and experimental observations show that the flowis captured qualitatively correctly.A method for numerical verification of the computational results hasbeen derived and applied to the computational results of the presentwork. The method is based on the conservation of a sub-set of the angularmomentum equations that is particularly important to swirlingflow in water turbines. The method is based on the fact that the discretizedangular momentum equations are not necessarily conservedwhen the discretized linear momentum equations are solved. The methodshows that the first-order hybrid discretization scheme cannot beused and that the second-order Van Leer discretization scheme needsimprovement to give quantitatively correct results in these kinds ofapplications