title: Towards Predictive Large-Eddy-Simulation-based Modeling of Reactive Multiphase Flows using Tabulated Chemistry
Creators: name: Dreßler, Louis Jons
Publisher: name: UNSPECIFIED
Year: 2021

description: Probably the strongest argument in favor of liquid fuels, compared to gaseous fuels, electrical batteries or mechanical energy storages, is their high energy density at ambient conditions. This contributed to the strong attention dedicated to combustion devices fueled with liquids in the last few decades. At present, liquid fuels are still the primary choice for transport and storage systems. However, in view of their detrimental impact on the environment, it is of the utmost importance to increase the overall efficiency of combustion-driven devices and simultaneously to minimize their environmental impact. From a practical standpoint, the combustion of liquids includes multiple interwoven processes, such as the gradual breakup of large liquid structures into small droplets, the dispersion and evaporation of these droplets, the mixture formation and the subsequent combustion process. With respect to technical applications, all of these processes generally occur under the influence of turbulence, a chaotic, strongly unsteady process, which involves a broad spectrum of time and length scales. The better understanding of these processes is crucial to reach the goals mentioned above. Numerical simulations, beside experimental investigations, play a key role in improving this understanding. In this work, the large eddy simulation (LES) approach is used and further developed to investigate turbulent spray combustion systems while consistently considering the turbulence-chemistry-droplets interaction processes. The LES is combined with a tabulated chemistry approach to represent the detailed kinetics of the combustion reaction. Beside the development of an interface to efficiently apply chemistry tabulation strategies within the finite volume code OpenFOAM, the present work implements and investigates two different approaches to model the interaction of the turbulence and chemistry in the context of LES: the artificially thickened flame (ATF) model and the Eulerian stochastic field (ESF) method. The methodologies are rigorously verified and validated, first in simple test-cases and then in turbulent single phase turbulent combustion. It is shown that the modeling framework is able to reproduce experimental measurements with great accuracy. The final step in this ladder of gradually increasing complexity is to apply the respective frameworks to spray combustion. Thereby, the multiphase system is treated using a two-way coupled Euler-Lagrange approach. For the liquid phase treatment, two novel approaches to represent the interaction of droplets with a thickened flame are proposed and evaluated. By taking into account the relative orientation of flame front and droplet movement using the proposed projection correction method, the overall consistency of the modeling framework is improved. Additionally, a novel strategy to compute turbulent spray combustion based on the ESF method coupled to the chemistry tabulation strategy is proposed. Its predictive capability is demonstrated and it is shown that this novel approach has great potential to evaluate classical turbulence-chemistry interaction models. Therefore, the developed methodologies constitute a significant achievement towards predictive simulations of spray combustion.