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@ARTICLE{AR-CFD-22-56, author = {Aniello, A. and Schuster, D. and Werner, P. and Boussuge, J.-F. and Gatti, M. and Mirat, C. and Selle, L. and Schuller, T. and Poinsot, T. and Ruede, U. }, title = {Comparison of a finite volume and two Lattice Boltzmann solvers for swirled confined flows}, year = {2022}, volume = {241}, pages = {105463}, doi = {10.1016/j.compfluid.2022.105463}, journal = {Computers and Fluids}, abstract = {A finite volume and two Lattice–Boltzmann unsteady, flow solvers using LES (Large Eddy Simulation) were compared in a swirling flow configuration, typical of aeronautical combustion chambers. Numerical results were validated against experimental data collected at EM2C laboratory by comparing pressure losses, mean and RMS velocity profiles on multiple planes and axial velocity spectra. Meshes and the overall numerical setups were individually adjusted for each code to obtain the targeted accuracy before comparing CPU efficiencies. Results confirm that the three LES codes provide high fidelity results, much better than usual RANS especially in terms of RMS data. The analysis of CPU performances shows that LBM (Lattice–Boltzmann Method) solvers are faster than the finite volume solver, even if CPU efficiencies remains of the same order of magnitude. In addition, strong scaling tests from 36 to 900 cores show that the finite volume solver scales more efficiently than the LBM codes, specially when the number of grid points per core is not sufficient.}, keywords = {CPU efficiency, Large Eddy Simulation, LBM and FVM comparison, Swirling flow}}

@ARTICLE{AR-PA-22-60, author = {Giraud, L. and Jing, Y-F. and Xiang, Y. }, title = {A Block Minimum Residual Norm Subspace Solver with Partial Convergence Management for Sequences of Linear Systems}, year = {2022}, number = {2}, volume = {43}, pages = {710-739}, doi = {10.1137/21M1401127}, journal = {SIAM Journal on Matrix Analysis and Applications}, abstract = {We are concerned with the iterative solution of linear systems with multiple right-hand sides available one group after another with possibly slowly varying left-hand sides. For such sequences of linear systems, we first develop a new block minimum norm residual approach that combines two main ingredients. The first component exploits ideas from GCRO-DR [Parks et al., SIAM J. Sci. Comput., 28 (2006), pp. 1651--1674], enabling us to recycle information from one solve to the next. The second component is the numerical mechanism for managing the partial convergence of the right-hand sides, referred to as inexact breakdown detection in IB-BGMRES [Robbé and Sadkane, Linear Algebra Appl., 419 (2006), pp. 265--285], that enables the monitoring of the rank deficiency in the residual space basis expanded blockwise. Next, for the class of block minimum norm residual approaches that relies on a block Arnoldi-like equality between the search space and the residual space (e.g., any block GMRES or block GCRO variants), we introduce new search space expansion policies defined on novel criteria to detect the partial convergence. These novel detection criteria are tuned to the selected stopping criterion and targeted convergence threshold to best cope with the selected normwise backward error stopping criterion, enabling us to monitor the computational effort while ensuring the final accuracy of each individual solution. Numerical experiments are reported to illustrate the numerical and computational features of both the new block Krylov solvers and the new search space block expansion polices.}, keywords = {hal-03546496v2}, url = {https://hal.inria.fr/hal-03546496v2}}

@ARTICLE{AR-CFD-22-61, author = {Crespo-Anadon , J. and Benito-Parejo, C.J. and Richard, S. and Riber, E. and Cuenot, B. and Strozzi, C. and Sotton, J. and Bellenoue, M. }, title = {Experimental and LES investigation of ignition of a spinning combustion technology combustor under relevant operating conditions}, year = {2022}, volume = {242}, pages = { 112204}, doi = {10.1016/j.combustflame.2022.112204}, journal = {Combustion and Flame}, abstract = {SAFRAN Helicopter Engines has developed the spinning combustion technology in which the burnt gases from one injector travel tangentially along the combustor annulus towards the neighboring injectors. Compared to a conventional design, this arrangement modifies the ignition process, which is a critical phase for aeroengines. In order to understand the ignition process in this technology, experiments and Large-Eddy Simulation (LES) have been performed in a cylindrical combustion chamber where the flow is injected tangentially (named Radius chamber). Three cases are considered with different strain and turbulence levels representative of real combustor flows. Micro calorimetry and the Background-Oriented Schlieren technique allows for detailed temporal measurements of energy deposited in the flame kernel. Pressure measurement and Schlieren imaging are used to study the flame propagation. LES are performed with a 19-species and 184-reactions analytically-reduced chemistry together with the thickened flame approach allowing the description of the first instants of ignition in a quasi-DNS mode and ensuing flame propagation. Both a static and dynamic formulations of the wrinkling factor to describe sub-grid scale chemistry-turbulence interaction are used. Results show that LES is able to capture the flame kernel formation and trajectory as well as the time to reach maximum pressure within an error of 10% when using a dynamic formulation. On the other hand, the static formulation of the wrinkling factor predicts the time for maximum pressure within a maximum error of 20%.}, keywords = {Ignition, Analytically Reduced Chemistry, LES, Spinning combustion technology}, pdf = {https://cerfacs.fr/wp-content/uploads/2022/06/CFD_Crespo_Comb_flame_AR_CFD_22_61.pdf}}

@ARTICLE{AR-PA-22-63, author = {Di Pietro, D.A. and Matalon, P. and Mycek, P. and Ruede, U. }, title = {High-order multigrid strategies for HHO discretizations of elliptic equations}, year = {2022}, volume = {in press}, 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}, url = {https://hal.archives-ouvertes.fr/hal-03531293/}}

@ARTICLE{AR-PA-22-48, author = {Lea, D.J. and While, J. and Martin, M.J. and Weaver, A.T. and Storto, A. and Chrust, M. }, title = {A new global ocean ensemble system at the Met Office: Assessing the impact of hybrid data assimilation and inflation settings}, year = {2022}, doi = {10.1002/qj.4292}, journal = {Quarterly Journal of the Royal Meteorological Society}, abstract = {We have developed a global ocean and sea-ice ensemble forecasting system based on the operational FOAM (Forecasting Ocean Assimilation Model) system run at the Met Office. The ocean model NEMO and the CICE sea-ice model run at 1/4° resolution and the system assimilates data using a three-dimensional variational assimilation (3DVar) version of NEMOVAR. This data assimilation (DA) system can perform hybrid ensemble/variational assimilation. A 36 member ensemble of hybrid-ensemble-variational assimilation systems with perturbed observations (values and locations) has been set-up, with each member forced at the surface by a separate member of the Met Office Global-Regional Ensemble Prediction System (MOGREPS-G). The unperturbed member is forced by atmospheric fields from the Met Office operational Numerical Weather Prediction (NWP) deterministic system. The system includes stochastic model perturbations and a Relaxation to Prior Spread (RTPS) inflation scheme. A control run of the system using an ensemble of 3DVars is shown to be generally reliable for sea level anomaly (SLA), temperature and salinity (the ensemble spread being a good representation of the uncertainty in the ensemble mean), although the ensemble is underspread in eddying regions. The ensemble mean gives a 4% reduction in error in SLA compared with the deterministic 3DVar system currently used operationally. The system was tested with different weights for the ensemble component of the hybrid background error covariance matrix and different inflation factors. The best results, in terms of short-range forecast error and ensemble reliability statistics, were obtained with hybrid three-dimensional ensemble variational DA (3DEnVar). The RTPS inflation scheme is shown to be beneficial in producing an appropriate ensemble spread in response to hybrid DA. 3DEnVar with an ensemble hybrid weight of 0.8 leads to a reduction of 20% (5%) in the ensemble mean error for SLA (profile temperature and salinity) compared with an ensemble of standard 3DVars. }}