An a priori DNS analysis of scale similarity based combustion models for LES of non-premixed jet flames

A Shamooni,T Faravelli,A Sadiki,A Cuoci

doi:10.1007/s10494-019-00099-9

A Shamooni, T Faravelli + Show 2 more

Open Access

https://doi.org/10.1007/s10494-019-00099-9

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Abstract

In this work, recently developed finite-rate dynamic scale similarity (SS) sub-grid scale (SGS) combustion models have been a priori assessed and compared with the Eddy Dissipation Concept (EDC) and “no model” approaches based on a Direct Numerical Simulation (DNS) database of a temporally evolving non-premixed jet flame. Two different filter widths, one placed in the inertial range and the other in the near dissipation range, have been used. The analyses were carried out in two time instants corresponding to instants of maximum local extinction and re-ignition. Conditional averaged filtered chemical source terms, conditioned on different parameters in the composition space, have been presented. Improvements are observed using the dynamic SS models compared to the two other approaches in the prediction of filtered chemical source terms of individual species while using larger filter widths. However, discrepancies still exists using the dynamic SS model on the turbulent/non-turbulent interfaces of the jet, mainly in the prediction of the oxidizer consumption rate.

Highlights

Combustion of fossil fuels is the primary source of energy production
An a priori analysis was carried out using Direct Numerical Simulation (DNS) databases of temporally evolving non-premixed jet flames, experiencing high levels of local extinction followed by re-ignition, with different Reynolds numbers
The “no model approach”, viz. ωnoModel (φ) = ω, neglecting sub-grid scale (SGS) effects are shown in these figures

Summary

Introduction

Combustion of fossil fuels is the primary source of energy production. the combustion of conventional fuels is prone to pollutant formation and emissions. An a priori analysis was carried out using DNS databases of temporally evolving non-premixed jet flames, experiencing high levels of local extinction followed by re-ignition, with different Reynolds numbers (the so-called cases L, M and H [15]). In their analyses using a fixed filter width (set equal to = 12 DNS ≈ 12ηf , with DNS the DNS [15] grid size and ηf the Favre averaged Kolmogorov length scale), improvements were observed in the prediction of filtered heat release rates compared to the non-dynamic models in the highest Reynolds flame. The results of the a priori analysis will be presented and final conclusions will be drawn

Dynamic SS models

EDC model

The DNS Database

Extinction time

Summary and Conclusions