arXiv subjects

Ambrus Both

Publications and source records attributed to Ambrus Both.

3 recordsLinked to original sources

arXiv2024

Analysis of thermodiffusive instabilities in hydrogen premixed flames using a tabulated flamelet model

Preferential diffusion plays a critical role in the evolution of lean premixed hydrogen flames, influencing flame surface corrugation and overall flame behavior. Simulating such flames with tabulated chemistry (TC) methods remains challenging due to the complexity of flame dynamics. A detailed assessment of flamelet-based manifolds for capturing these dynamics is still needed. This work incorporates preferential diffusion via mixture-averaged molecular diffusion within TC to study the propagation and structure of freely propagating hydrogen flames influenced by intrinsic instabilities. Model performance is evaluated against detailed chemistry (DC) calculations, focusing on linear and non-linear regimes and sensitivity to pressure and temperature variations. The impact of mesh resolution on flame response is also examined to assess the method's capabilities without subgrid models. The linear regime is analyzed through the dispersion relation, revealing that higher temperature or pressure extends the range of wave numbers accurately predicted by the model, although some overprediction of flame wrinkling in stable regions is observed. The nonlinear regime is assessed by comparing global flame parameters and flame structure to reference solutions, showing that the model captures key flame descriptors with relative errors under 20%. Overall, the model effectively reproduces key effects governing flames with thermodiffusive instabilities, offering a viable alternative to DC at a significantly reduced computational cost.

physics.flu-dyn↗

arXiv2022

A portable coding strategy to exploit vectorization on combustion simulations

The complexity of combustion simulations demands the latest high-performance computing tools to accelerate its time-to-solution results. A current trend on HPC systems is the utilization of CPUs with SIMD or vector extensions to exploit data parallelism. Our work proposes a strategy to improve the automatic vectorization of finite element-based scientific codes. The approach applies a parametric configuration to the data structures to help the compiler detect the block of codes that can take advantage of vector computation while maintaining the code portable. A detailed analysis of the computational impact of this methodology on the different stages of a CFD solver is studied on the PRECCINSTA burner simulation. Our parametric implementation has proven to help the compiler generate more vector instructions in the assembly operation: this results in a reduction of up to 9.3 times of the total executed instruction maintaining constant the Instructions Per Cycle and the CPU frequency. The proposed strategy improves the performance of the CFD case under study up to 4.67 times on the MareNostrum 4 supercomputer.

cs.DC↗

arXiv2022

Evaporation of volatile droplets subjected to flame-like conditions

This work assesses Lagrangian droplet evaporation models frequently used in spray combustion simulations, with the purpose of identifying the influence of modeling decisions on the single droplet behavior. Besides more simplistic models, the evaluated strategies include a simple method to incorporate Stefan flow effects in the heat transfer (Bird's correction), a method to consider the interaction of Stefan flow with the heat and mass transfer films (Abramzon-Sirignano model), and a method to incorporate non-equilibrium thermodynamics (Langmuir-Knudsen model). The importance of each phenomena is quantified analytically and numerically under various conditions. Evaporation models ignoring Stefan flow are found to be invalid under the studied conditions. The Langmuir-Knudsen model is also deemed inadequate for high temperature evaporation, while Bird's correction and the Abramzon-Sirignano model are identified as the most relevant for numerical studies of spray combustion systems. Latter is the most elaborate model studied here, as it considers Reynolds number effects beyond the empirical correlation of Ranz and Marshall derived for low-transfer rates. Thus, the Abramzon-Sirignano model is identified as the state of the art alternative in the scope of this study.

physics.flu-dyn↗