Novel Evolutions of Turbines for Hydropower through the Use of a New Simulation tool – NETHUNS

In the Etruscan mythology, Nethuns was the god of waters. Etruscan civilization is in particular known for its hydraulic engineering. However, even if hydraulic engineering exists for more than two millennia, the linked scientific field, namely fluid mechanics, is still one of the most important challenges in modern physics. Indeed, due to the chaotic character of turbulent flows, nobody in physics has really been able to analyze it mathematically satisfactorily in spite of its importance to various industrial applications.

It is in this context that General Electric Hydro France and the LEGI lab will perform the NETHUNS project (for Novel Evolution of Turbines for Hydropower through the Use of a New Simulation tool). This project aims to develop a new synergy between fundamental research and industrial development to deeply understand hydrodynamic instabilities happening in hydropower plant, and then be able to propose innovative solutions to design turbines. To achieve this objective, the project will develop an innovative simulation tool to take full advantage of the new opportunities given by the exponential rise in computational power to perform significant breakthroughs in this field. The project will address all the challenges linked with the advanced analysis of flow in hydropower turbine, based on high-fidelity simulations. The project will be then composed of two main axes: (i) the physical analysis of hydrodynamic phenomena, and (ii) the development of new simulation strategies.

The main objective of new turbines is to be able to efficiently work on a broader range of operating points, to allow a transition towards the growth of other intermittent renewable energies. It needs to deeply understand the chaotic behavior of turbulent flows in hydropower turbine, and to be able to mitigate their consequences. Two main physical issues will be addressed during the project. First, the appearance of an intense vortex structure in the turbine draft tube will be studied, because it is known that this structure can strongly increase the head losses in the overall turbine, and then limit its efficiency. Second, the specific case of pump-turbine system will be considered. Pump-turbines are the main tool used to store electricity and to bring flexibility to the grid. For some operating points, a pump-turbine is unstable during the pumping phase, due to the appearance of a rotating stall in the turbine distributor. Deep knowledge of this phenomenon is needed to mitigate its effect.

To expect breaking-through on physical understanding of such complex flows, an innovative simulation approach has to be developed. The objective of this new tool is to obtain exhaustive unsteadiness flow description at an affordable computational cost. This will be possible only if numerical techniques and modeling approaches are improved. In this project, numerical developments will be done in the YALES2 code, one of the most efficient codes for unsteady flow simulations. The objective is to develop accurate and robust numerical methods to avoid additional computational cost due to numerical stability constraint. Moreover, since it is not yet possible to explicitly solve the overall spatiotemporal scales of an industrial turbulent flows, modeling of some scales is mandatory. The objective is to develop a modeling strategy to allow an optimal reliability, at a sufficient level of flow description with a reduced computational cost.

A new synergy between the academic and the industrial partners is planned with a direct implication of the industrial partner in the code development, and its use in applications. A part of the NETHUNS project will be also devoted to training in the field of “Advanced Numerical Simulations for the Design of Energy Systems” at various levels: by continuous training for engineers, by promoting network of postdoc researchers, PhD students and engineers, and by enforcing this field in the ENSE3 engineering school program.