Transient 3D CFD Simulation of a Pelton Turbine—A State-of-the-Art Approach for Pelton Development and Optimisation

The complex flow conditions in Pelton turbines make it challenging to gain detailed insight into the local flow processes. However, CFD methods offer vast potential for developing and optimising Pelton turbines due to these flow conditions. In a comprehensive examination, a six-nozzle prototype Pelton turbine with 19 buckets has been investigated using 3D CFD simulations. First, the steady simulations of the manifold and the unsteady runner simulation have been performed with a mesh-based, commercial CFD code, whereby a two-equation turbulence model and the homogeneous two-phase model were used. Then, to limit the simulation time, symmetry was applied in the runner simulation, and also a strategic definition of the mesh element size in selected blocks of higher interest. Subsequently, the simulation results were analysed. Based on the first simulation results, the geometry of the distributor was modified in an iterative process to reduce losses and improve the jet shape. For the improvement of the latter, a characteristic number was introduced to quantify the secondary flows upstream of the nozzles, which act negatively on the jet shape. Furthermore, the results of the runner simulation were analysed with special regard to the jet-bucket interaction from the start to the end of the impingement cycle of a particular bucket. Finally, a potential efficiency increase could be derived from the summary.