In this case study the customer asked MSI to carry out a complete structural and hydraulic analysis of a new application for a Pelton turbine. These impulse-type turbines are a favorite choice due to its high efficiency in converting kinetic energy from water jets into mechanical energy, suitability for high-head, low-flow applications, and minimal environmental impact, making it ideal for small-scale and run-of-river installations.
Structural Integrity
MSI carried out a detailed fluid-structure analysis of the Pelton turbine under nominal operation in the software STAR-CCM+. The buckets of a Pelton turbine are under cyclic load conditions as they pass through the high velocity water jet. Cyclic fatigue failure is a major concern. The analysis revealed an exact prediction of the maximum and mean Van Mises Stresses occurring in the wheel to enable a determination of fatigue failure limits.
Detailed Windage Losses by Dry and Wet Phase
The complex physics of the multi-phase flow in a Pelton turbine make an experimental determination of hydraulic and aerodynamic windage losses very difficult if not impossible. Whilst the overall efficiency of shaft power to fluid power can be easily measured, it is difficult to measure how much loss splashing water and swirling air is creating. MSI's Fluids Engineering developed a CFD technique to determine the windage losses based on wet and dry phases from the transient CFD analysis. The diagram below shows the average braking torque breakdown by wet and dry phase.
Cavitation Prediction
Cavitation is the formation of vapor in regions of low pressures, usually zones where the fluid has been accelerated to high velocities. Cavitation can occur in Pelton turbines where the bucket intersects the high velocity water jet and can cause erosion on the turbine wheel. The CFD analysis deployed the industry standard Schnerr-Sauer cavitation model in STAR-CCM+. The animation below shows the predicted vapor formation (in red) for a water temperature of 22 C.
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