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Coupling of a direct quadrature based sectional method of moments with Large Eddy Simulation (LES) for describing polydisperse reacting spray systems

Subject Area Energy Process Engineering
Fluid Mechanics
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 427460734
 
Final Report Year 2024

Final Report Abstract

This work used the large eddy simulation (LES) approach and further developed LES to investigate turbulent spray combustion systems. Beside the development of an interface to efficiently apply chemistry tabulation strategies within the open source code OpenFOAM, this project implemented and investigated two different approaches to model the interaction of the turbulence and chemistry: the artificially thickened flame model and the Transported filtered probability density function according to the Eulerian stochastic field method. The WALE Subgrid Scale (SGS) model was used to describe the SGS structures of the turbulent fluid flow. Based on this LES plateform, this project aimed at the development, implementation, verification, validation and evaluation of an advanced Euler-Euler method in which the evaporating droplets are tracked using an Eulerian methodology, such as the direct quadrature-based sectional moment method (DQbSMOM). Thereby coalescence process as well as droplet-droplet interactions had to be modelled. During the first steps of adapting the available RANS-based tool to LES framework, the preliminary tests with some existing breakup and coalescence kernels revealed that various different formulations yield significantly different results. A thermodynamically rational treatment appeared compelling while being associated with complex and burdensome modelling efforts. Since this might modify strongly the main direction of the project, the applicant undertook therefore to improve the concept in order to enhance the quality of the outcome while ensuring the simplicity of the modelling. He then included the in-nozzle flow along with an interface tracking algorithm that allows to better capture the whole liquid atomisation which governs all the subsequent processes. In this respect, the primary and secondary breakup are naturally captured without particular modelling. This results in a LES-based Volume of Fluid (VOF) method that replaces not only the DQb-SMOM method coupled to the E-MMF as proposed, but also the previously suggested MMEF formalism associated with high modelling efforts. In addition, the Euler Multi-Size Moment (EMSM) approach became unnecessary allowing to save modelling expenses and computational costs. To track the generated polydispersed particles/droples three approaches have been adopted: (a) the pure LES-based VOF; (b) a full T-FDF coupled with a Lagrangian particle tracking (LPT); (c) a novel seamless coupling technique of the LES-based VOF with the LPT including phase change modelled in both VOF and LPT. Focusing on the tabulated chemistry, the FG-based tabulation approach has been improved by integrating two specific features: (1) the presence of heat loss during droplet evaporation, (2) the essential properties for the evaluation of irreversibilities in combustion systems through the entropy generation analysis (EGA) approach. Two classes of configurations have been selected for model validation. The Sandia Flames D, E, F and a SCR-configuration were used especially for the evaluation of the EGA. Three configurations were utilized to validate the modelling suggested. These are (a) CORIA Rouen swirled Spray Burner (CRSB) system which is one of the target configurations of the “Turbulent Spray Combustion (TCS)” workshop; (b) Liquid jet in hot cross-flow as experimentally investigated by Shaw et al. (2022); and (c) Single droplets of Hexane and Decane, respectively. Owing to the improvement of the concept of this project, all the objectives have been successfully achieved.

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