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@ARTICLE{AR-PA-23-7, author = {Ambekar, A.S. and Schwarzmeier, C. and Ruede, U. and Buwa, V.V. }, title = {Particle-resolved turbulent flow in a packed bed: RANS, LES, and DNS simulations}, year = {2023}, number = {1}, volume = {69}, pages = {e17615}, doi = {10.1002/aic.17615}, journal = {AICHE Journal}, abstract = {Packed bed reactors are widely used to perform solid-catalyzed gas-phase reactions and local turbulence is known to influence heat and mass transfer characteristics. We have investigated turbulence characteristics in a packed bed of 113 spherical particles by performing particle-resolved Reynolds-averaged Navier–Stokes (RANS) simulations, Large Eddy Simulation (LES), and Direct Numerical Simulation (DNS). The predictions of the RANS and LES simulations are validated with the lattice Boltzmann method (LBM)–based DNS at particle Reynolds number (Rep) of 600. The RANS and LES simulations can predict the velocity, strain rate, and vorticity with a reasonable accuracy. Due to the dominance of enhanced wall-function treatment, the turbulence characteristics predicted by the ε-based models are found to be in a good agreement with the DNS. The ω-based models under-predicted the turbulence quantities by several orders of magnitude due to their inadequacy in handling strongly wall-dominated flows at low Rep. Using the DNS performed at different Rep, we also show that the onset of turbulence occurs between (Formula presented.).}}

@ARTICLE{AR-CFD-23-16, author = {Agostinelli, P.W. and Laera, D. and Chterev, I. and Boxx, I. and Gicquel, L.Y.M. and Poinsot, T. }, title = {Large eddy simulations of mean pressure and H2 addition effects on the stabilization and dynamics of a partially-premixed swirled-stabilized methane flame}, year = {2023}, volume = {249}, pages = {112592}, doi = {10.1016/j.combustflame.2022.112592}, journal = {Combustion and Flame}, abstract = {This work analyzes pressure and hydrogen enrichment effects on the stabilization and combustion dynamics of a partially-premixed swirled-stabilized methane flame operated at 1, 3 and 5 bar, with H admixture up to 40% by volume. Large Eddy Simulations (LES) are performed to analyze flame stabilization and dynamics for all cases. When pressure is increased, both turbulence and chemical time scales are reduced leading to smaller turbulent scales and thinner flames which makes LES modeling challenging. To ensure that all flames are resolved similarly in the tested pressure range, the dynamic formulation of the thickened flame model (DTFLES) is used here with a Static Mesh Refinement (SMR) strategy. An Analytically Reduced Chemistry (ARC) scheme is employed to describe CH-H/Air chemistry. LES is validated against experimental multi-kHz repetition-rate OH* chemiluminescence, OH Planar Laser Induced Fluorescence (PLIF), stereoscopic Particle Image Velocimetry (sPIV) and pressure recordings. The dynamics of the different flames are then addressed. First, the impact of hydrogen at atmospheric pressure is investigated. While the reference natural gas flame (1 bar, 0% H) presents a lifted M-shape with a strong Precessing Vortex Core (PVC), 40% H-enrichment modifies the flame which becomes an attached V-shape, with a weakened PVC and the triggering of a thermoacoustic oscillation at the combustion chamber first acoustic mode. Second, the impact of mean pressure is analyzed by fixing the H-enrichment while increasing the mean pressure to 3 and then 5bar. As the pressure increases, the flame assumes a more compact M-shape. It is proven that the interaction with the turbulent smallest scales is not affected by pressure: Karlovitz number is constant. On the contrary, the flame response to the large turbulent structures is modified: Damkhler number reduces when mean pressure increases. If strong flame/PVC interactions are observed at atmospheric pressure leading to flame tip/root roll-up and local quenching, a more coherent flame is observed when pressure is raised. Furthermore, for these points, the thermoacoustic oscillation coupled with the first chamber acoustic mode rapidly disappears and stable conditions are recovered.}, pdf = {https://cerfacs.fr/wp-content/uploads/2023/01/Combustion_Flame_Agostinelli_AR_CFD_23_16.pdf}}

@ARTICLE{AR-PA-23-18, author = {Goux, O. and Pfeffer, J. and Blazquez, A. and Weaver, A.T. and Ablain, M. }, title = {A mass conserving filter based on diffusion for Gravity Recovery and Climate Experiment (GRACE) spherical harmonics solutions}, year = {2023}, doi = {10.1093/gji/ggad016}, journal = {Geophysical Journal International}, abstract = {Over the past two decades, the GRACE (Gravity Recovery and Climate Experiment) and GRACE Follow-On mission (GRACE-FO) have provided monthly measurements of the gravity field as sets of Stokes coefficients, referred to as spherical harmonics solutions. The variations of the gravity field can be used to infer mass variations on the surface of the Earth, mostly driven by the redistribution of water. However, unconstrained GRACE and GRACE-FO solutions are affected by strong correlated errors, easily identified as stripes along the North-South direction in the spatial domain. Here, we develop a filter based on the principle of diffusion to remove correlated errors and access the underlying geophysical signals. In contrast to many filters developed for this task, diffusion filters allow a spatially variable level of filtering that can be adapted to match spatially variable signal-to-noise ratios. Most importantly, the formalism of diffusion allows the implementation of boundary conditions, which can be used to prevent any flux through the coastlines during the filtering step. As mass conservation is enforced in the filter, global indicators such as trends in the global mean ocean mass are preserved. Compared with traditional filters, diffusion filters ensure the consistency of the solution at global and regional scales for ocean applications. Because leakage errors occurring during the filtering step are suppressed, better agreement is found when comparing diffusion-filtered spherical harmonic solutions with mascon solutions and independent estimates based on altimetry and in situ data.}}

@ARTICLE{AR-CFD-23-19, author = {Gallen, L. and Riber, E. and Cuenot, B. }, title = {Investigation of soot formation in turbulent spray flame burning real fuel}, year = {2023}, volume = {in press}, pages = {112621}, doi = {10.1016/j.combustflame.2023.112621}, journal = {Combustion and Flame}, abstract = {This work uses Large Eddy Simulation (LES) combined with an accurate chemical description to predict soot formation in a turbulent spray flame burning real fuel at atmospheric conditions. Understanding and being able to predict soot formation in practical configurations burning complex liquid fuel is essential for the design of engines meeting present and future environmental requirements. The prediction of soot formation with numerical simulations has been mostly limited to academic configurations burning light gaseous fuel. This is explained by the numerical cost of (i) the fuel oxidation chemistry including soot precursors like Polycyclic Aromatic Hydrocarbons (PAH), and (ii) the modeling of two dispersed phases, i.e., the liquid fuel spray and the soot particles. In this work, an Analytically Reduced Chemistry (ARC) for real fuels is proposed to allow a direct integration of accurate combustion chemistry including PAH in the compressible LES solver AVBP. The ARC model is coupled with a Lagrangian particle tracking approach for both the fuel droplets and the soot, including for the latter the description of the complex physical and chemical processes driving the particle evolution. Validation is first performed in a one-dimensional ethylene/air flame configuration, experimentally studied in the literature at several operating points. The numerical profiles of both the soot volume fraction and the soot diameter are in good agreement with measurements. This allows to apply the LES methodology to the sooting swirled turbulent liquid JetA-1/air combustor measured at UTIAS. Very satisfying predictions for both the flow dynamics and the soot production are obtained. The analysis of the results brings valuable new insights on the interaction between fuel droplets, turbulent combustion, PAH and soot evolution in such complex flames.}}

@ARTICLE{AR-PA-23-4, author = {Di Pietro, D.A. and Matalon, P. and Mycek, P. and Ruede, U. }, title = {High-order multigrid strategies for Hybrid high-order discretizations of elliptic equations}, year = {2023}, number = {1}, volume = {30}, pages = {e2456}, doi = {10.1002/nla.2456}, journal = {Numerical Linear Algebra with Applications}, abstract = {This study compares various multigrid strategies for the fast solution of elliptic equations discretized by the Hybrid High-Order method. Combinations of h-, p-and hp-coarsening strategies are considered, combined with diverse intergrid transfer operators. Comparisons are made experimentally on 2D and 3D test cases, with structured and unstructured meshes, and with nested and non-nested hierarchies. Advantages and drawbacks of each strategy are discussed for each case to establish simplified guidelines for the optimization of the time to solution. }, keywords = {Elliptic partial differential equation, hybrid high-order, multigrid, coarsening strategy}}