An a priori assessment of the Partially Stirred Reactor (PaSR) model for MILD combustion |
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Authors: | Salvatore Iavarone Arthur Péquin Zhi X Chen Nguyen Anh Khoa Doan Nedunchezhian Swaminathan Alessandro Parente |
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Institution: | 1. Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK;2. Aero-Thermo-Mechanics Laboratory, École Polytechnique de Bruxelles, Université Libre de Bruxelles, Avenue F.D Roosevelt 50, Brussels 1050, Belgium;3. Combustion and Robust Optimization Group (BURN), Université Libre de Bruxelles and Vrije Universiteit Brussel, Bruxelles, Belgium;4. Department of Mechanical Engineering and Institute for Advanced Study, Technical University of Munich, Boltzmannstrasse 15, Garching 85748, Germany |
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Abstract: | Moderate or Intense Low-oxygen Dilution (MILD) combustion has drawn increasing attention as it allows to avoid the thermo-chemical conditions prone to the formation of pollutant species while ensuring high energy efficiency and fuel flexibility. MILD combustion is characterized by a strong competition between turbulent mixing and chemical kinetics so that turbulence-chemistry interactions are naturally strengthened and unsteady phenomena such as local extinction and re-ignition may occur. The underlying physical mechanisms are not fully understood yet and the validation of combustion models featuring enhanced predictive capabilities is required. Within this context, high-fidelity data from Direct Numerical Simulation (DNS) represent a great opportunity for the assessment and the validation of combustion closure formulations. In this study, the performance of the Partially Stirred Reactor (PaSR) combustion model in MILD conditions is a priori assessed on Direct Numerical Simulations (DNS) of turbulent combustion of MILD mixtures in a cubical domain. Modeled quantities of interest, such as heat release rate and reaction rates of major and minor species, are compared to the corresponding filtered quantities extracted from the DNS. Different submodels for the key model parameters, i.e., the chemical time scale τc and the mixing time scale τmix, are considered and their influence on the results is evaluated. The results show that the mixing time scale is the leading scale in the investigated cases. The best agreement with the DNS data regarding the prediction of heat release rate and chemical source terms is achieved by the PaSR model that employs a local dynamic approach for the estimation of the mixing time scale. An overestimation of the OH species source terms occurs in limited zones of the computational domain, characterized by low heat release rates. |
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