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@ARTICLE{AR-CFD-19-46, author = {Tagliante, F. and Poinsot, T. and Pickett, L.M. and Pepiot, P. and Malbec, L.-M. and Bruneaux, G. and Angelberger, C. }, title = {A conceptual model of the flame stabilization mechanisms for a lifted Diesel-type flame based on Direct Numerical Simulation and experiments}, year = {2019}, number = {March}, volume = {201}, pages = {65-77}, journal = {Combustion and Flame}, abstract = {This work presents an analysis of the stabilization of diffusion flames created by the injection of fuel into hot air, as found in Diesel engines. It is based on experimental observations and uses a dedicated Direct Numerical Simulation (DNS) approach to construct a numerical setup, which reproduces the ignition features obtained experimentally. The resulting DNS data are then used to classify and analyze the events that allow the flame to stabilize at a certain Lift-Off Length (LOL) from the fuel injector. Both DNS and experiments reveal that this stabilization is intermittent: flame elements first auto-ignite before being convected downstream until another sudden auto-ignition event occurs closer to the fuel injector. The flame topologies associated to such events are discussed in detail using the DNS results, and a conceptual model summarizing the observation made is proposed. Results show that the main flame stabilization mechanism is auto-ignition. However, multiple reaction zone topologies, such as triple flames, are also observed at the periphery of the fuel jet helping the flame to stabilize by filling high-temperature burnt gases reservoirs localized at the periphery, which trigger auto-ignitions.}, keywords = {DNS, Lift-off length, Flame stabilization, Auto-ignition, Triple flame, Diesel combustion}, url = {https://doi.org/10.1016/j.combustflame.2018.12.007}}

@ARTICLE{AR-CMGC-19-50, author = { Trucchia, A. and Mattei, M.R. and Luongo, V. and Frunzo, L. and Rochoux, M. }, title = {Surrogate-based uncertainty and sensitivity analysis for bacterial invasion in multi-species biofilm modeling}, year = {2019}, volume = {73}, pages = {403-424}, doi = {10.1016/j.cnsns.2019.02.024}, journal = {Communications in Nonlinear Science and Numerical Simulation}, pdf = {https://cerfacs.fr/wp-content/uploads/2019/03/GLOBC-Article-Trucchia-etal_CNSNS19b.pdf}}

@ARTICLE{AR-CFD-19-25, author = {Collin-Bastiani, F. and Marrero-Santiago, J. and Riber, E. and Cabot, G. and Renou, B. and Cuenot, B. }, title = {A joint experimental and numerical study of ignition in a spray burner}, year = {2019}, number = {4}, volume = {37}, pages = {5047-5055}, doi = {10.1016/j.proci.2018.05.132}, journal = {Proceedings of the Combustion Institute}, abstract = {Partly due to stringent restrictions on pollutant emissions, aeronautical engine manufacturers target lean operating conditions which raise new difficulties such as combustion stability as well as ignition and re- ignition at high altitude. The injection of liquid fuel introduces additional complexity due to the spray-flame interaction. It is then crucial to better understand the physics behind these phenomena and to develop the capacity to predict them in an industrial context. In this work, a comprehensive joint experimental and nu- merical investigation of the academic swirled-confined version of the KIAI-Spray burner is carried out. Experimental diagnostics, such as Phase Doppler Anemometry (PDA), Planar Laser Induced Fluorescence (OH-PLIF), high-speed visualization and high-speed particle image velocimetry (HS-PIV), together with Large Eddy Simulations coupled to Discrete Particle Simulations are used to study spray flame structure and spray ignition. The analysis of the swirled-stabilized spray flame highlights the main effects of the presence of droplets on the turbulent combustion, and the complementarity and validity of the joint experiment and simulation approach. Ignition sequences are then studied. Both experiment and simulation show the same behaviors, and relate the flame kernel evolution and the possible success of ignition to the local non reacting flow properties at the sparking location, in terms of turbulence intensity and presence of droplets}, keywords = {Spray flame, Ignition, Laser diagnostics, Large Eddy Simulation}, url = {https://doi.org/10.1016/j.proci.2018.05.132}}

@ARTICLE{AR-CFD-19-29, author = {Wissocq, G. and Sagaut, P. and Boussuge, J.-F. }, title = {An extended spectral analysis of the lattice Boltzmann method: modal interactions and stability issues}, year = {2019}, number = {March}, volume = {380}, pages = {311-333}, doi = {10.1016/j.jcp.2018.12.015}, journal = {Journal of Computational Physics}, abstract = {An extension of the von Neumann linear analysis is proposed for the study of the discrete-velocity Boltzmann equation (DVBE) and the lattice Boltzmann (LB) scheme. While the standard technique is restricted to the investigation of the spectral radius and the dissipation and dispersion properties, a new focus is put here on the information carried by the modes. The technique consists in the computation of the moments of the eigenvectors and their projection onto the physical waves expected by the continuous linearized Navier–Stokes (NS) equations. The method is illustrated thanks to some simulations with the BGK (Bhatnagar–Gross–Krook) collision operator on the D2Q9 and D2V17 lattices. The present analysis reveals the existence of two kinds of modes: non-observable modes that do not carry any macroscopic information and observable modes. The latter may carry either a physical wave expected by the NS equations, or an unphysical information. Further investigation of modal interactions highlights a phenomenon called curve veering occurring between two observable modes: a swap of eigenvectors and dissipation rate is observed between the eigencurves. Increasing the Mach number of the mean flow yields an eigenvalue collision at the origin of numerical instabilities of the BGK model, arising from the error in the time and space discretization of the DVBE.}, keywords = {Lattice Boltzmann, von Neumann analysis}, url = {https://doi.org/10.1016/j.jcp.2018.12.015}}

@ARTICLE{AR-CFD-19-26, author = {Collin-Bastiani, F. and Vermorel, O. and Lacour, C. and Lecordier, B. and Cuenot, B. }, title = {DNS of spark ignition using Analytically Reduced Chemistry including plasma kinetics}, year = {2019}, number = {4}, volume = {37}, pages = {5057-5064}, doi = {10.1016/j.proci.2018.07.008}, journal = {Proceedings of the Combustion Institute}, abstract = {In order to guarantee good re-ignition capacities in case of engine failure during flight, it is of prime interest for engine manufacturers to understand the physics of ignition from the spark discharge to the full burner lightning. During the ignition process, a spark plug delivers a very short and powerful electrical discharge to the mixture. A plasma is first created before a flame kernel propagates. The present work focuses on this still misunderstood first instants of ignition, i.e., from the sparking to the flame kernel formation. 3D Direct Numerical Simulations of propane-air ignition sequences induced by an electric discharge are performed on a simple anode-cathode set-up. An Analytically Reduced Chemistry (ARC) including 34 transported species and 586 irreversible reactions is used to describe the coupled combustion and plasma kinetics. The effect of plasma chemistry on the temperature field is found to be non-negligible up to a few microseconds after the spark due to endothermic dissociation and ionization reactions. However, its impact on the subsequent flame kernel development appears to be weak in the studied configuration. This tends to indicate that plasma chemistry does not play a key role in ignition and may be omitted in numerical simulations.}, keywords = {Spark ignition, Plasma kinetics, Analytically Reduced Chemistry}, url = {https://doi.org/10.1016/j.proci.2018.07.008}}