Papers by Francois Avellan
Conference proceedings, 2019
While operating at part load, Francis turbines feature a precessing cavitation vortex rope in its... more While operating at part load, Francis turbines feature a precessing cavitation vortex rope in its draft tube. The precession of this vortex in the elbow of the draft tube acts as a pressure pulsation source which frequency can match the first hydroacoustic eigenfrequency of the hydraulic system in some cases. Resonance phenomenon can be predicted by using reduced scale physical model tests and numerical simulations, but it remains challenging. This paper proposes a procedure to estimate the risk of part load resonance at the early stage of a hydropower project. The proposed procedure uses the hydroacoustic properties of a given reduced scale physical model and applies them to a large number of turbine designs and power plant configurations to assess the risk of resonance for each one of them. Results show that resonance are likely to occur in hydropower plants in a certain range of turbine rated head and rated discharge values. These results can then indicate if more detailed investigations in some specific hydropower projects are necessary.
Journal of physics, Apr 4, 2017
Hydropower plants may be required to operate in synchronous condenser mode in order to supply rea... more Hydropower plants may be required to operate in synchronous condenser mode in order to supply reactive power to the grid for compensating the fluctuations introduced by the intermittent renewable energies such wind and solar. When operating in this mode, the tail water in the Francis turbine or pump-turbine is depressed below the runner by injecting pressurized air in order to spin in air to reduce the power consumption. Many air-water interaction phenomena occur in the machine causing air losses and a consequent power consumption to recover the air lost. In this paper, the experimental investigation of the sloshing motion in the cone of a dewatered Francis turbine performed by image visualization and pressure measurements is presented. The developed image post processing method for identifying the amplitude and frequency of the oscillation of the free surface is described and the results obtained are illustrated and discussed.
Journal of physics, Apr 4, 2017
IOP conference series, Mar 27, 2019
The numerical investigation of the unsteady flow patterns around a Pelton bucket can be helpful t... more The numerical investigation of the unsteady flow patterns around a Pelton bucket can be helpful to improve the overall turbine efficiency by optimizing the bucket design based on identified loss mechanisms. Since the flow is highly turbulent, modeling the effect of turbulence can bring about improved predictions. In this paper, two RANS-based eddy viscosity models (namely the standard and realizable k-ε) have been implemented as a module in a particle-based in-house solver, GPU-SHPEROS. A scalable wall function based on the log-law has been utilized to model the flow in the near-wall region. The solver has been accelerated on GPUs and is based on the Finite Volume Particle Method (FVPM), which is a locally conservative and consistent particle-based method including many of the attractive features of both particle-based methods (e.g. SPH) and conventional mesh-based methods (e.g. FVM). As a mesh-free method based on the Arbitrary Lagrangian Eulerian (ALE) formulation, FVPM is robust in handling free surface flows and large boundary deformations, such as the ones found in rotating Pelton buckets. The validation of the turbulence models implementation within FVPM is presented for internal and free surface flows. Then, the effectiveness of the turbulence models in the case of rotating Pelton buckets is assessed by comparing the predicted torque time histories to experimental data acquired on a model-scale test rig.
Bulletin of the American Physical Society, Nov 21, 2021
Computer Methods in Applied Mechanics and Engineering, Apr 1, 2017
Journal of Fluids Engineering-transactions of The Asme, Jul 15, 2016
The investigation of the rotating stall phenomenon appearing in the HYDRODYNA pump-turbine reduce... more The investigation of the rotating stall phenomenon appearing in the HYDRODYNA pump-turbine reduced scale model is carried out by performing a large-scale large eddy simulation (LES) computation using a mesh featuring approximately 85 × 106 elements. The internal flow is computed for the pump-turbine operated at 76% of the best efficiency point (BEP) in pumping mode, for which previous experimental research evidenced four rotating stall cells. To achieve an adequate resolution near the wall, the Reynolds number is decreased by a factor of 25 than that of the experiment, by assuming that the flow of our interest is not strongly affected by the Reynolds number. The computations are performed on the supercomputer PRIMEHPC FX10 of the University of Tokyo using the overset finite-element open source code FrontFlow/blue with the dynamic Smagorinsky turbulence model. It is shown that the rotating stall phenomenon is accurately simulated using the LES approach. The results show an excellent agreement with available experimental data from the reduced scale model tested at the EPFL Laboratory for hydraulic machines. The number of stall cells as well as the propagation speed agree well with the experiment. Detailed investigations on the computed flow fields have clarified the propagation mechanism of the stall cells.
Experiments in Fluids, May 15, 2018
Renewable Energy, Apr 1, 2020
Journal of Physics: Conference Series, 2017
At partial load and overload conditions, Francis turbines are subjected to hydraulic instabilitie... more At partial load and overload conditions, Francis turbines are subjected to hydraulic instabilities that can potentially result in high dynamic solicitations of the turbine components and significantly reduce their lifetime. This study presents both experimental data and numerical simulations that were used as complementary approaches to study these dynamic solicitations. Measurements performed on a reduced scale physical model, including a special runner instrumented with on-board strain gauges and pressure sensors, were used to investigate the dynamic phenomena experienced by the runner. They were also taken as reference to validate the numerical simulation results. After validation, advantage was taken from the numerical simulations to highlight the mechanical response of the structure to the unsteady hydraulic phenomena, as well as their impact on the fatigue damage of the runner.
International Journal of Multiphase Flow, Mar 1, 2019
IOP conference series, Jun 1, 2021
In the framework of the XFLEX HYDRO H2020 European Project, one of the demonstrators focuses on t... more In the framework of the XFLEX HYDRO H2020 European Project, one of the demonstrators focuses on the implementation of the hydraulic short-circuit on the pump storage power plant of Grand-Maison owned by Electricité De France (EDF). The Grand-Maison power plant is a two-level plant production with one plant located above the downstream reservoir and equipped with four Pelton turbines; a second plant located downstream the reservoir and equipped with eight reversible pump-turbines. Hydraulic short circuit consists in running pumps and turbines in the meantime to balance the energy consumption of the pumps compared to the grid. Such an operating mode allows increasing the flexibility of the power plant and targeting the requirement of balancing the intermittent production due to the growing of new renewable energies such as wind and solar power plants. The hydraulic short-circuit operating mode leads to a change in the flow paths in the penstocks and junctions compared to the normal turbine or pump modes. Indeed, compared to the pump mode, this mode will lead to a flow derivation at the junction between the penstocks directed to the Pelton units and the penstocks directed to the upper reservoir. As this mode have not been scheduled at the beginning of the power plant construction, it is necessary to quantitatively assess the singular head losses generated at the junction to be able to simulate the complete behaviour of the power plant by means of a 1D model. CFD simulations are carried out with the Fluent software for several configurations of hydraulic short-circuit defined by the ratio of flow rate deviated to the Pelton turbines.
International Journal of Multiphase Flow, Aug 1, 2018
International Journal of Multiphase Flow, Feb 1, 2019
IOP conference series, Mar 1, 2014
In this paper, we present a 3-D FVPM which features rectangular top-hat kernels. With this method... more In this paper, we present a 3-D FVPM which features rectangular top-hat kernels. With this method, interaction vectors are computed exactly and efficiently. We introduce a new method to enforce the no-slip boundary condition. With this boundary enforcement, the interaction forces between fluid and wall are computed accurately. We employ the boundary force to predict the motion of rigid spherical silt particles inside the fluid. To validate the model, we simulate the 2-D sedimentation of a single particle in viscous fluid tank and compare results with benchmark data. The particle resolution is verified by convergence study. We also simulate the sedimentation of two particles exhibiting drafting, kissing and tumbling phenomena in 2-D and 3-D. We compare the results with other numerical solutions.
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Papers by Francois Avellan