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Author: search.filters.author.Bravo, LuisLanguage: search.filters.language.English

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    A Priori Assessment of Deconvolution-based Models for Large Eddy Simulation Sub-Filter Scale Turbulent Stress Tensors in Compressible Homogeneous Isotropic Turbulence
    (AIP, 2026-05-01)
    This study presents an a priori evaluation of deconvolution-based sub-filter scale (SFS) models for the turbulent stress tensor in large eddy simulation (LES) of compressible homogeneous isotropic turbulence. The assessed closures include the approximate deconvolution model (ADM), the direct deconvolution model (DDM), the discrete direct deconvolution model (D3M), and the dynamic iterative approximate deconvolution (DIAD) model. These approaches reconstruct unfiltered flow variables from spatially filtered data, enabling direct estimation of unresolved SFS stresses. Their performance is compared with classical closures, namely, the dynamic Smagorinsky model and the dynamic mixed model. High-resolution direct numerical simulation data are filtered using a top-hat kernel and downsampled to a coarser LES-like grid, after which an explicit Gaussian filter is applied to emulate an explicitly filtered LES framework. This methodology provides a stringent a priori assessment by accounting for filter attenuation and grid-truncation effects. Each deconvolution-based model is examined independently, including a systematic analysis of its parameters, and multiple filter-to-grid ratios re considered to quantify scale-separation effects. Model performance is assessed using correlation coefficients, relative errors, scatter plots, probability density functions, and power spectra of individual SFS stress components. The results show that deconvolution-based closures consistently outperform classical models, achieving higher correlations, lower reconstruction errors, and improved recovery of scale-dependent features. Indeed, DDM exhibits the highest reconstruction fidelity, while ADM, D3M, and DIAD show strong agreement with the reference stresses. These findings establish that deconvolution-based models are robust and physically consistent model closures for LES of compressible turbulent flows.
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    Influence of obstacle separation distance on the acceleration of premixed methane/air flames in a closed channel
    (Springer Science and Business Media B.V., 2025)
    Flame acceleration plays an important role in determining the onset of deflagration-to-det­onation transition (DDT) phenomenon that is relevant to novel pressure-gain propulsion and explosion safety research. Accordingly, this work explores the influence of the separa­tion distance between obstacles (S) inside a 1050 mm closed duct on the acceleration of premixed flames fueled by a stoichiometric methane/air mixture at 40 kPa pressure. The studied duct geometry features a 96 mm x 96 mm square cross section and includes five obstacles along the wall with a 75% blockage ratio, each delineated by side dimensions of 96 mm x 96 mm and square holes of 48 mm x 48 mm. Experimental and direct numerical simulations (DNS) techniques are employed here to investigate the flame acceleration dy­namics under different operating conditions. More specifically, high-speed video captures the dynamics of the flame front evolution from experiments, while DNS are carried out using the PeleC fully compressive Navier Stokes solver, including finite-rate chemistry and adaptive mesh refinement (AMR). A comparison between experimental and numerical results for S = 1.0 Dₕ shows reasonable agreement in flame tip velocity and reduced posi­tion, supporting the applicability of a two-dimensional DNS model like the one employed here. In contrast, for S = 1.5 Dₕ the numerical results fail to reproduce the experimentally observed flame structure and acceleration, likely due to missing three-dimensional effects. Numerical simulations for different S values ranging from 0.75 to 1.5 Dₕ reveal that ob­stacle spacing has a strong influence on flame acceleration mechanisms. As S increases indeed, the flame shifts from geometry-constrained jetting to instability-driven propaga­tion involving vortex generation and pressure-wave interactions. The case with S = 1.25 Dₕ yields the highest flame tip velocity, even though the one with S = 1.5 Dₕ exhibits greater vorticity and pressure amplitudes. This is attributed to the reduced flame–vortex coupling coherence in the S = 1.5 Dₕ case, which results in more chaotic flame dynamics and lower flame acceleration efficiency. These results offer new insight into the mechanisms of flame acceleration under confinement and highlight obstacle spacing as a key design parameter for optimizing performance and safety in combustion systems.
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