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Better analysis tools for water power turbo-machinery and marine propellers

EU-funded researchers advanced state-of-the-art computational tools to enhance the design of hydraulic rotating machinery and marine propellers.
Better analysis tools for water power turbo-machinery and marine propellers
Computational fluid dynamics (CFD) is now widely used for designing hydraulic equipment for hydropower projects. Once the specialised tool of the aerospace industry, CFD is now indispensable tool to increase performance and reduce costs of hydraulic machinery.

CFD application extends beyond turbine design to also detect and identify hydraulic operating problems on existing machines. The EU-funded project ACCUSIM was established to develop reliable numerical tools and methods for detailed analysis of turbulent flows to facilitate the design of powerful hydro-machinery and marine propellers. “Numerical modelling and flow analysis of water turbines, pumps and marine propellers provides a means of identifying the cause of the problem and develop alternatives, reducing the number of manufactured model-size runners and thus making hydromachine performance testing less expensive,” notes Dr Aljaž Škerlavaj, project coordinator.

Advanced modelling of rotating machinery

Over the last 15 years, development of effective and easily applicable numerical methods for flow simulations has significantly increased. Flow analysis models of rotating and non-rotating turbine parts along with more powerful computing platforms enabled coupled analysis of the turbine as a whole in a reasonable amount of time. Advanced turbulent models of unsteady flows allowed researchers to obtain numerical predictions that show good agreement with experimental results.

While state-of-the-art CFD simulations mainly rely on Reynolds-averaged Navier-Stokes turbulence models, certain classes of flows are better covered by models that resolve part of the turbulence spectrum in at least a portion of the numerical flow domain. Such methods are termed scale-resolving simulation models.

Project researchers focused in particular on modelling unsteady turbulent flows and cavitation effects in Francis turbines and axial turbines using scale resolving turbulence models. Until now, the design of these turbines has been tackled with steady-state simulations as transient simulations require significant computational effort. Cavitation phenomena refer to the formation of vapour cavities in liquid regions where pressure is low. In propellers and pumps, cavitation causes a great deal of noise, damage, vibrations, and a loss of efficiency. Application of calibrated cavitation models was key in achieving accurate predictions of cavitating flow in hydraulic turbines and marine propellers.

Dissemination activities

The ACCUSIM team participated in two test case workshops. The first one was a workshop about prediction of cavitation and propeller performance in oblique flow. Researchers were given access to the geometry and necessary initial and boundary conditions. The second workshop was the first of a series of three workshops where researchers took part in open-trial experiments. Researchers were given access to the complete dataset for the design of a Francis turbine. The first workshop concentrated on modelling the turbine steady-state operation, whereas the other two looked at transient operating conditions such as load variation and start-stop, and the fluid-structure interaction.

Using general purpose CFD codes such as ANSYS CFX and OpenFOAM, the project team succeeded in generating one of the most accurate simulation data at both workshops – for the propeller regarding cavitation pattern shape and propeller thrust, whereas for the turbine regarding efficiency, hydraulic head, mass flow rate and torque predictions.

ACCUSIM results were disseminated through many publications targeting the scientific community. Lectures at schools, tutorials, conferences and summer school were used to reach the public. The project website contains more information.

Subjects

Life Sciences

Keywords

ACCUSIM, computational fluid dynamics (CFD), hydro turbine, scale-resolving simulation, ANSYS CFX, OpenFOAM
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