Simulating innovative hydroturbine design to eliminate multiple prototypes and reduce financial risk

Supporting unique turbine design

Mechanical Solutions, Inc. (Mechanical Solutions) is an engineering consultancy and Siemens Digital Industries Software partner that specializes in turbomachinery design and troubleshooting. It offers advanced computational fluid dynamics (CFD) expertise to manufacturers, allowing them to focus on the hydropower solutions they design and build.

Its hydroturbine machinery is mostly used for energy generation from creeks and rivers and is customized specifically to the installation location as the amount of water and pressure can vary greatly.

In one case, a Pelton turbine was developed for a reservoir power plant. Water is pumped into underground storage when excess energy is available, then released to drive the turbine for generating electricity. The geological depth of the reservoir leads to elevated water temperatures due to geo-thermal heating and significantly higher pressure compared to typical hydropower reservoirs. The turbine had to be designed to handle the intense high-pressure water jets impacting the turbine buckets and to mitigate the increased risk of cavitation under these extreme conditions.

A turbine operating in such conditions was a novelty for the manufacturer, so it was necessary to understand whether an existing design would meet the structural requirements or need to be modified. It would have been far too expensive and time-consuming to conduct trial-and-error prototyping, so Mechanical Solutions carried out a complete virtual analysis of the design before any hardware was built.

Mechanical Solutions used Simcenter™ STAR-CCM+™ software to simulate both the flow and the structural behavior of the turbine. Simcenter STAR-CCM+, which is part of the Siemens Xcelerator business platform of software, hardware and services, is a powerful CFD solution that provides sophisticated multiphysics simulation capabilities. It integrates solid mechanics with finite element models (FEMs) for applications like nonlinear geometry, thermal expansion and fluid-structure interaction.

Ensuring structural integrity

Pelton turbines, designed to harness the energy of high-pressure velocity water jets to generate mechanical power, are engineered for a lifespan of up to 50 years. To ensure durability and reduce maintenance costs, it is crucial to minimize wear and degradation on the components.

According to Boris Kubrak, director of computational fluids engineering at Mechanical Solutions, there were two key areas of investigation. “First we needed to verify the structural integrity of the design by ensuring that its stiffness was adequate to withstand the operational stresses imposed on the turbine,” he says. “We had to be certain that the attachment of the buckets was robust enough to prevent failure or detachment during operation. Then we had to carry out a full analysis of the fluid dynamics because when water is hot it is much more prone to cavitation, which would damage the turbine.”

Complete fatigue analysis

Mechanical Solutions used Simcenter STAR-CCM+ to model the complete turbine structure and simulate the interaction of high-speed, high-temperature water jets with the buckets. This analysis enabled Mechanical Solutions to evaluate the resulting dynamic stress distributions and their impact on the structural integrity of the system. “In a Pelton turbine like this, the pressure fluctuates cyclically, making fatigue a big challenge,” says Kubrak.

“Simcenter STAR-CCM+ gives us a complete picture of where and how frequently high stresses occur. Based on that information, we can derive a fatigue analysis that is valuable to the customer. This allows us to accurately predict the number of cycles the components can withstand without failure based on the stresses they experienced.”

Kubrak says that carrying out all the analysis with one solution is a big advantage. “The beauty of Simcenter STAR-CCM+ is that we can do everything within one application without coupling to a solid solver,” he explains. “Without this we would have to calculate the forces and then give the data to a separate structural engineer to analyze the effect. Instead, we can carry out a complete fluid structure interaction analysis in one shot, which saves us a lot of time.”

This was also significant as the design of the turbine changed during development. “Once you build the baseline model in Simcenter STAR-CCM+, it’s very easy to make modifications,” says Kubrak. “We had to be adaptable to whatever changes the customer needed to make, and thanks to the integrated nature of the software, where everything is modeled within a single platform, implementing the required adjustments only took half a day. Using previous methods with multiple applications, it would take at least two or three times longer to make the changes.”

Simulation drives innovation

The fatigue analysis showed the final design of the turbine was within the required boundaries. Kubrak also carried out a parametric study to calculate under what conditions the turbine might suffer fatigue. “This is the first turbine operating in these particular conditions so it’s unknown territory,” he says. “The parametric study enabled us to identify the pressures and temperatures that would compromise the structure. This allowed us to provide the customer with a safe operating range to ensure the system remains within secure limits.”

With the simulation results giving the customer full confidence in their design, they were able to proceed with constructing the turbine for an extended live test run. “A proof of concept needs to be performed that shows how well the turbine will operate,” says Kubrak. “The analysis with Simcenter STAR-CCM+ meant the turbine only needed to be built once, as they could be sure it wouldn’t fail. Otherwise, multiple prototypes would have been required with design adjustments between each test run. This would have been expensive and taken much longer.”

Having such an accurate picture of how the turbine will hold up also leads to big savings in maintenance and downtime. When it is time to perform maintenance, manufacturers will know exactly what needs to be evaluated as the simulation analysis will show which parts will have been subject to the most stress.

Kubrak is confident that Simcenter STAR-CCM+ will continue to play a vital role at Mechanical Solutions and in the industry. “Without simulation, this project wouldn’t have been possible as there would have been too much financial risk for the customer and their investors,” he explains. “Simcenter STAR-CCM+ has enabled this innovative concept to become a reality. Without it, many ideas would never get past the early stages as the risk would be too great, so it’s an important solution for experimentation and innovation.”