15th European Conference on Turbomachinery Fluid dynamics & Thermodynamics

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Hydraulics Machine



Simon Joßberger - Institute of Fluid Mechanics and Hydraulic Machinery, University of Stuttgart, Germany
Stefan Riedelbauch - Institute of Fluid Mechanics and Hydraulic Machinery, University of Stuttgart, Germany


Double regulated Kaplan turbines with adjustable guide vanes and runner blades offer a high degree of flexibility and good efficiency for a wide range of operating points. However, this also leads to a complex geometry and flow guidance with, for example, vortices of different size and strength. The flow in a draft tube is especially challenging to simulate mainly due to flow phenomena like swirl, separation and strong adverse pressure gradient and a strong dependency on the upstream flow conditions. Standard simulation approaches with RANS turbulence models, a relatively small mesh size and large time step size often fail to correctly predict the performance and can even lead to wrong tendencies in the overall behaviour. Results of a scale resolving hybrid RANS-LES simulation on a block structured mesh of about 400 million hexahedral elements of a double regulated five blade model Kaplan turbine are analysed to reveal occurring flow phenomena and physical effects. The simulation results are validated with experimental data, consisting of global results like total head and torque and phase resolved three-dimensional PIV measurements of the velocity in the cone and both diffusers of the draft tube. The comparison of flow fields of the measurements, the highly resolved hybrid RANS-LES simulation and a standard RANS simulation with about 20 million elements allows an assessment of the importance of resolved and unresolved flow phenomena and effects.

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