Numerical simulation of vortex induced pressure fluctuations in the runner of a Francis turbine at deep part load conditions

For hydropower applications far off-design operating points like deep part load are more and more investigated, as these turbines can play a key role for the compensation of fluctuations in the electrical grid. In this study the single-phase simulation results of a Francis turbine at model scale are investigated for three mesh resolutions with the commercial CFD software ANSYS CFX. For the investigated deep part load operating point the typical inter-blade vortices can be observed. Further vortex structures are on the one hand traveling upstream close to the suction side and are on the other hand a result of a flow detachment at the runner trailing edge. The evaluation of the mesh resolution shows that a mesh refinement especially in the region of the inter-blade vortices results in a better prediction of the pressure minimum of these vortices. The strong scaling test indicates an acceptable scaling up to 1536 cores for the mesh with 56 million cells. For the mesh with 82 million cells the scaling is acceptable even up to 2048 cores. A comparison of the MPI methods Open MPI and HMPT MPI showed that the latter is 16.5% slower.