It is an activity in the field of engineering sciences that is culturally close to G-INP (all members of the research teaching team at Ense3 participate). It concerns conventional hydraulic turbines or emerging turbines for the hydroelectric and wind power sectors. In the first case, research is focused on reproducing the complex 3D unsteady flows in these machines. In the second case, they aim to propose and optimize new machines and to study the problem of their installation in the park. This axis concentrates collaborations with major industrial groups (EDF, GE/Alstrom, CNES, SNECMA, Artelia, Cetim) and benefits from a large flow of doctoral candidates (9 theses defended, 4 in progress, 2 post-doctorates). Interactions exist with the Most and Meige teams. This focus was strengthened in 2018 with the recruitment of P.-L. Delafin (MCF – G INP).
A turbomachine is a machine that allows an exchange of energy between its rotating solid part and an external fluid. This definition concerns conventional hydraulic machines (pumps and turbines, inductors) and new systems such as hydro turbines to harness the energy of marine and river currents. The research carried out in our team on turbomachinery is a joint research project with industrial partners. The challenge of the energy transition has revitalized this activity. The challenge of this research is to be able to reproduce and predict the unsteady 3D flows developing in these machines when they undergo operating conditions for which they were not designed. For conventional hydraulic machines, the need to increase their flexibility must be met by using them in a pressure-flow range far from their operating point. This is the case, for example, for the part-load operation of turbines, designed to compensate for the intermittency of renewable sources (wind, hydropower, hydrodynamics), or for the switch between pumping and turbining modes. These variations in operating conditions lead to unstable hydrodynamic regimes and increased dynamic stresses on the solid parts of the machines, with or without cavitation. For turbine turbines, blade profile optimization is also a crucial issue. At the fleet level, the interaction between machines and wakes is studied to optimize its architecture. On a larger scale, an important issue is the environmental impact of large marine wind or hydro turbine farms on marine or air currents and the ecosystem. New generations of turbomachinery are also being studied from a purely thermodynamic point of view, and this is a new theme for LEGI.
In 2016, the 28th symposium on hydraulic machines and systems was held in Grenoble, France, organized by R. Fortes-Patella (G-INP, SHF) under the auspices of the International Association for Hydro-Environment Engineering (IAHR), and attended by 330 participants from 32 countries.
The assessment of the work of the team members concerned by this axis is as follows.
Turbulent unsteady flows in complex geometries, in both cavitating and non-cavitating regimes, have been studied numerically (C. Jacquet, U. Jese, B. Charrière, with the support of the Supergrid Energy Transition Institute – GE/Alstom, University of Ljubliana); unpublished calculations in cavitating regimes have been made for Kaplan turbines in pumping mode (F. Turi). A thesis was also devoted to the study of experimental identification methods and the validation of simulation models of transfer functions of cavitation systems and POGO shock absorbers (A. Simon, CNES / Snecma). In this context, the experimental method known as the “3 sensors” was used to measure the speed of sound in a single- and two-phase environment, over a range between 100 m/s and 1400 m/s[Simon et al. 2016].
Digital and experimental work has been carried out on part-load flows in Francis turbines to highlight interblade vortexes and to implement a blade fatigue model (S. Bouajila FUI “Platform” carried by GE). The experiments, conducted on a reduced instrumented model, concluded that the modelled flow was consistent with observations of the position of the inter-tube vortices and the amplitude of pressure fluctuations (with the exception of high frequency fluctuations). The rate of fatigue damage attributed to vortexes between blades is very much higher than that due, for example, to the flare phenomenon. This confirms the dangerousness of inter-vane vortices during very partial flow operating regimes.
3D modelling of transverse flow turbine farms (G. Mercier, V. Clary) combined with hydrodynamic tunnel tests has shown that upstream turbulence reduces Reynolds dependence on the power delivered by the turbine. The turbine wake is not very sensitive to upstream turbulence, and the torque and drag are calculated with good accuracy; the wake obtained by modelling compares well with the experiment beyond a distance equal to four times the turbine diameter, but the speed is overestimated in the nearby wake (V. Clary, T. Oudart, ANR EMR-ITE funding). A test campaign on an axial flow turbine is in preparation.
Fluid-structure interaction for transverse flow turbines with deformable wings is also a theme addressed by the team; while flexible profiles reduce the risk of damage due to fatigue, they are often accompanied by a reduction in the power output. The challenge is to optimize these structures. The tests carried out in LEGI tunnels on flexible oscillating profiles led to an increase in the driving force for an unchanged bending force. A calculation code modelling fluid-structure interaction on an oscillating flexible profile is under development, in collaboration with the University of Magdeburg (S. Hoerner).
Finally, two valorization initiatives were undertaken, thanks to the support of SATT Linksium. The first, concerning a new type of transverse flow turbine (principle patented in 2017, PCT extension in 2018, support from the Carnot Institute), is proof of concept. The Coriolis platform will serve as a traction basin for the associated model. The measured efficiency of the turbine will then determine the search for funders for an industrialization of the apparatus. The second approach, concerning the study of twin vertical axis twin turbine floating turbines, inspired by a new patented design by LEGI researchers (Most and Energetics team), has resulted in an optimal architecture allowing a real technological breakthrough. It is one of the team’s highlights, since all the stages of invention, maturation and development led by LEGI members have been successfully completed (N. Guillaud, M. Guilhot, G. Maurice, ANR EMR-ITE financing).
The energy optimization of the machines also concerns their thermodynamic operation. Rankine cycles with organic fluid are relevant when a hot source is available at low or medium temperature (< 300°C): geothermal power plants, biomass combustion, heat recovery from effluents. The disadvantages that limit the deployment of such a technology are on the one hand the energy performance of the thermodynamic cycle and on the other hand the environmental constraints caused by the use of certain organic fluids. We are studying (in collaboration with the CEA) a new way to overcome these two difficulties: the use of a mixture of fluids instead of a pure fluid as working fluid (zeotropic mixtures). A specific turbine technology was experimentally implemented with a new generation of working fluid that is very interesting from an environmental point of view (Q. Blondel).
(N. Caney, S. Barre, P-L Delafin, E. Goncalvès, F. Jousselin, R. Fortes – Patella, T. Maitre, C. Pellone)