The performances of ground- and airborne transport vehicles, wind turbines, rotating machinery, combustors and many other configurations are strongly affected by flow separation and consequently benefit from efficient separation control. Further performance enhancements by passive and active devices are requested by industry. This proposal targets a model-based separation control strategy working robustly in experiment for a range of operating conditions. Focus is placed on nominally 2D configurations at different Reynolds numbers. The flow control demonstrators cover the range from laminar to turbulent separation, including a low Reynolds-number smooth backward facing step (Poitiers, water tunnel), a similar configuration at medium Reynolds-number (Orleans, wind tunnel) and a high Reynolds number ramp (Lille, wind tunnel). The physical understanding is augmented by reduced-order models (ROM) from experimental data (Poitiers), URANS simulations (Orleans), and LES computations (Lille). The flow is manipulated with passive vortex generators and active control from periodic excitation to closed-loop design using ROM. We import and adapt promising strategies having worked in other experiments. The breadth of control plants will enable the proposal consortium to distil the key actuation mechanisms and arrive at good practices for robust separation control for various conditions. As one educational benefit, the consortium aims at involving students from the International Master of Turbulence program (Lille, Poitiers). On a French national level, the studies shall define experimental benchmark demonstrators for more refined modelling and control strategies, to be maintained and presented in the GDR 2502.

The Spark Ignition (SI) engine represents 70% of light duty vehicles worldwide and should still represent 50% in 2030. For this reason, reducing CO2 emissions of SI engines is of primary importance to contribute mitigating the global warming. For this purpose, the technology favored today by engine manufacturers is downsizing, which consists in reducing the displacement and increasing the specific power by using a turbocharger. The fuel saving potential of up to 20% offered by this technology is however limited in practice due to an increased occurrence of abnormal combustions (knock and super-knock) which lead to using sub-optimal spark timings. A key measure for limiting the occurrence of abnormal combustion is to increase the EGR (Exhaust Gas Recirculation) rate from presently 5% to reach values as high as 20% and even 30%. This allows substantially reducing abnormal combustions but leads to larger cycle to cycle variability and decreased heat release rates. In order to reach such high EGR rates, complex strategies have to be developed (aerodynamics, injection targeting etc…), the design and optimization of which increasingly rely on Computational Fluid Dynamics (CFD). Recent research clearly showed that existing combustion models fail for EGR rates larger than 10% in downsized SI engines. MACDIL proposes acquiring an unprecedented understanding of combustion under intermediate (15 to 25%) and high (beyond 25%) EGR rates and under pressure and temperature conditions representative of turbocharged SI engines, and to capitalize it in the form of both LES and RANS models integrated respectively in the reference LES research AVBP and the industrial RANS code CONVERGE. The major scientific challenges addressed by MACDIL to reach its ambitious objectives is the absence of sufficient knowledge on turbulent flames under such extreme conditions, the lack of adapted chemical kinetics, as well as the absence of experimental studies due to the practical difficulty with high pressure and temperature flame measurements. Concerning experiments, a unique set-up called NOSE (New One Shot Engine) will allow for the first time to study diluted combustion, both at low pressure and temperature in order to support LES model development, and at high pressure and temperature conditions for providing validation data for the developed models. This experiment will provide flame visualizations and a global comparison with CFD (in terms of pressure) but it won’t give access to the flame surface properties. For this reason, Direct Numerical Simulations (DNS) of a reduced scale NOSE configuration will be performed to provide detailed local flame statistics for orienting and supporting the LES combustion model development. The resulting LES models will first be validated against NOSE data, before being evaluated on an existing downsized research engine. Experimental measurements of the local effective flame speed at such conditions are also impossible. MACDIL thus proposes exploiting ab-initio calculations for formulating chemical schemes. The latter will be used to generate tables of planar and effective laminar flame speeds which constitute key input parameters in the combustion models to be developed. For simplicity, the experiments and CFD simulations of MACDIL will be conducted with isooctane as a fuel and N2 as a diluent. But kinetic modeling will also consider a surrogate fuel of gasoline and real EGR (including CO2 and H2O). As a final step, the combustion models developed within MACDIL will be adapted for RANS, and integrated into the industrial CFD code CONVERGE. This will allow the industrial partners to apply the MACDIL models to real downsized engines of interest to them, to evaluate their performance under high dilutions, and thus assess the benefit they offer for their future engine developments.

Our project aims at developping mathematically rigorous approaches to neuroscience considering single neurons as well as interconnected neuronal populations. Our target is to conduct the mathematical analysis of existing models where there is still much work to be done and to enrich the modelling by proposing new models. The presence of neuroscientists in our project will facilitate the validation of the mathematical models. The members of our project gather internationally renowned competence in mathematics as well as neuroscience. A lot of available studies have been conducted by simulations. Although this approach has certainly been fruitful and must be pursued, we it is limited and new results coming from a profound mathematical analysis are necessary. We center on partial differential equations (pdes) and probability. Even the classical models in neuroscience raise profound mathematical questions at the frontier of present mathematical knowledge ; we plan to conduct their study theoretically as well as numerically. One originality of our project is to integrate the various dynamical levels of the nervous system. For one single neuron the question is to describe large excursions of its electrical membrane potential from its rest value due to ionnic chemical reactions. Two biologists, Hodgkin and Huxley, proposed a four dimensional nonlinear system of reaction-diffusion equations with several time scales. Travelling and standing waves, oscillatory and asymptotic behaviour for this system is still today a challenging problem both theoretically and numerically that we address in this project. It is now clear that stochastic models are necessary to model experimental observations: the intrinsically stochastic ionic channel mechanism, constant synaptic efficacy, synchronization or resonance are observed only in stochastic conditions. We consider multidimensional stochastic models obtained by adding a random perturbation to a deterministic model of Hodgkin-Huxley type disregarding space propagation (or simplified versions in dimension 2 or 4). We search for the law of the first exit time of this process from a domain, for oscillating regimes and resonance induced by noise and investigate long time behaviour. We will have to face highly degenerate non gradient stochastic systems with non globally Lipschitz coefficients. Existing results do not apply. One dimensional Leaky Integrate and Fire (LIF) models will also be considered. Numerical stochastic schemes are necessary for their first passage time above a threshold : no accurate nor fast scheme is presently available. We will address this question. We also aim at developing stochastic models including space propagation. This amounts to introduce stochastic pdes models; it is a challenge both theoretically and numerically. There is no tradition to some reference models for populations of interconnected neurons. We are interested in synchronization, spontaneous activity, decision-making, dynamical probabilistic inference, information processing. We plan to study synchronization through the Kuramoto model in the light of recent results on out-of-equilibrium systems and disordered media. We also aim at undertaking the mathematical study of original models derived experimentally by neuroscientists in our group or foreign collaborators to describe respectively spontaneous activity and decision-making. Specific difficulties in pdes arise: specific non linearities, irrelevance of existing methods, non gradient Fokker-Planck equations. We also plan to develop models for the interaction of cortical micro-colums built on non linear Fourier integral operators. Recent studies lead by one of the neuroscientists in our group have shown that probabilistic models of dynamic inference can accurately account for various aspects of perception. One of the main theoretical difficulties in dynamical probabilistic inference is the exponential growing of necessary memory resources. Our goal is to examine several solutions to simplify the dynamical probabilistic computation on large set of variables. Perception and decision making result from information processing between several groups of neurons. Actually a complete mathematical formalism of information processing by a population of neurons is still missing. We would like to show that brain activities such as perception, memory, action, decision and adaptation can be interpreted in the light of non-equilibrium thermodynamics.

Energy transfer from a plasma to a substrate is a real issue in plasma processing. The understanding of the mechanisms responsible for the heat transfer is relevant and can help optimizing processes. - At GREMI, young researchers (Anne-Lise THOMANN and Rémi DUSSART) working on low pressure plasma processes (sputtering deposition, cryogenic etching of silicon ...) had an interest on the energy transfer from the plasma to the substrate during processes: A.L. Thomann used to study the growth regime of metal thin films synthesized by plasma sputtering. It has been shown that the film formation depends on the flux and energy of plasma ions incoming onto the surface during the growth, and on the kinetic energy of the condensing metal atoms. However quantification of the observed effects was missing. R. Dussart and its colleagues have evidenced the building of a passivation layer on etched silicon surface. This layer is destroyed during the etching process by thermal effects. - At the time that such questions arise, a researcher (Nadjib SEMMAR), specialist of thermal mechanisms joined the GREMI lab. After many discussions and brainstorming, we decided to initiate a new team in the lab to study and to measure the energy flux involved in the plasma/surface interaction. - - New ideas of diagnostics and measurements are born partly because the team is composed of researchers coming from different disciplines. - - Anne-Lise THOMANN (CNRS) is a specialist of materials science: she works on the elaboration and characterization of thin films deposited by low pressure plasmas. - - Remi DUSSART (Associate professor at the University of Orleans) used to work on capillary discharges for high energy photon production. He now works on cryogenic etching in low pressure plasmas. - - Nadjib SEMMAR (Associate professor at the University of Orleans) is a physicist specialized on thermal transfers. He used to work at the Lermab Laboratory at Nancy during eight years on the energetic of systems. He now works on the modelization of the laser-materials interaction and on the experimental characterization of the energy transfer. - To help us mounting and testing the experiments, Jacky MATHIAS, engineer (CNRS) joined the team. He is engineer specialized in Optical devices and works on the development of new diagnostics and reactors. - An engineer assistant, Yves Tessier, specialist in Electronics will also work on this project especially to install the data acquisition of the new diagnostic recently developed. - - The experience and the different origin of each of us is a real benefit for this project. Because we have complementary capabilities in plasma and materials science and energetics we were able to propose a new approach of plasma/surface interaction study involving the direct measurement of the energy transfers. Two ATIP proposals (CNRS) have already been proposed in the 3 last years. Although the subject was qualified as a very interesting and relevant, it was not selected. But we think that the project did not have the maturity of today. The team is now clearly identified in the lab and a plasma reactor is dedicated to this experiment. Its autonomy is now total, but the team needs the recognition of the ANR to really expand its activities. A post doc will be appreciated on this new subject to participate to the experiments. - - The role of each member of the team is clearly identified: - Jacky MATHIAS and Yves TESSIER will take part to the experiment installation and to the diagnostic construction. - Nadjib SEMMAR will take part to the design of the proposed new diagnostic to make some direct estimation of the energy flux. He has a good background on calibration methods using black bodies. One of them has been made in the lab and is dedicated to this project. He will also participate to the modelisation of heat flux transfer when a sample is mounted on the diagnostic. - Rémi DUSSART will be involved in the plasma characterization b