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High-fidelity Large Eddy Simulations (LES) are performed to study the effect of hydrogen injection on a lean turbulent CH 4 /Air premixed flame. An Analytically Reduced Chemistry (ARC) mechanism is used to achieve a detailed description of CH 4 /Air-H 2 chemistry. First, a validation of this kinetic scheme against the detailed GRI-Mech 3.0 mechanism is presented considering both simplified and complex transport properties. When hydrogen is added to the mixture, large variations of the mixture Prandtl and of the N 2 Schmidt numbers are observed depending on the local species concentration, features that are missed by simplified models. LES is then applied to study the structure and stabilization mechanisms of a lean (φ = 0.8) premixed CH 4 /Air swirled flame enriched with hydrogen by using different transport modeling strategies. First, the fully premixed CH 4 /Air case is considered and results are found to validate the LES approach. In agreement with experiments, a classical V-shape flame is stabilized in the low-velocity region near the flame holder created by a central recirculation zone (CRZ). Then, hydrogen enrichment is achieved injecting 2% of the CH 4 thermal power with a central fuel injection lance. Both premixed and diffusion flame branches are present in this case, impacting flame stabilization and angle. The flame root the main premixed flame stabilized by a diffusion flame kernel created by the injected hydrogen reacting with the oxygen in excess of the premixed stream. Moreover, the H 2 consumed with the remaining oxygen in burnt gases leads to the formation of a second flame branch inside the CRZ which is responsible of an increase of the flame angle. Given the high concentration of hydrogen, an impact of the molecular transport models is observed on the flame lift-off height highlighting the importance of using complex transport properties in any LES involving hydrogen combustion.

Global warming, climate change and pollution are burning environmental issues. To reduce the carbon footprint of the aviation sector, aeronautical companies have been striving to lower engine emissions via the development of reliable lean combustors. In this context, effort has been devoted to the better understanding of various flame dynamics with emphasis on thermoacoustic instabilities, lean blow-off and extinctions. In line with this effort, Safran Helicopter Engines has recently developed and patented the revolutionary spinning combustion technology (SCT) for its next generation of combustors. This technology has indeed great flexibility when it comes to ignition and blow-off capabilities. To better understand the various physical mechanisms occurring in a SCT combustor, a joint numerical and experimental analysis of the flame stabilization in this spinning combustion technology framework has been devised. On the experimental side, the NTNU atmospheric annular combustor has been modified to introduce a relevant azimuthal component of velocity while operating under premixed fuel conditions, following the SCT concept. Note that to reduce temperature at the backplane of the chamber, film cooling is incorporated to avoid fuel injector damage. On the numerical side, high fidelity Large Eddy Simulations of the test bench have been carried out with the

The design challenge of reliable lean combustors needed to decrease pollutant emissions has clearly progressed with the common use of experiments as well as large eddy simulation (LES) because of its ability to predict the interactions between turbulent flows, sprays, acoustics, and flames. However, the accuracy of such numerical predictions depends very often on the user's experience to choose the most appropriate flow modeling and, more importantly, the proper spatial discretization for a given computational domain. The present work focuses on the last issue and proposes a static mesh refinement strategy based on flow physical quantities. To do so, a combination of sensors based on the dissipation and production of kinetic energy coupled to the flame-position probability is proposed to detect the regions of interest where flow physics happens and grid adaptation is recommended for good LES predictions. Thanks to such measures, a local mesh resolution can be achieved in these zones improving the LES overall accuracy while, eventually, coarsening everywhere else in the domain to reduce the computational cost. The proposed mesh refinement strategy is detailed and validated on two reacting-flow problems: a fully premixed bluff-body stabilized flame, i.e., the VOLVO test case, and a partially premixed swirled flame, i.e., the PRECCINSTA burner, which is closer to industrial configurations. For both cases, comparisons of the results with experimental data underline the fact that the predictions of the flame stabilization, and hence the computed velocity and temperature fields, are strongly influenced by the mesh quality and significant improvement can be obtained by applying the proposed strategy.

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