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%0 Thesis
%A Denker, Dominik
%T Gradient trajectory analysis of reacting turbulent flows
%I RWTH Aachen University
%V Dissertation
%C Düren
%M RWTH-2021-01043
%@ 978-3-8440-7739-1
%B Berichte aus der Strömungstechnik
%P Online-Ressource (xix, 151 Seiten) : Illustrationen, Diagramme
%D 2020
%Z Druckausgabe: 2020. - Auch veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2021
%Z Dissertation, RWTH Aachen University, 2020
%X In this thesis, reacting turbulent flows are analyzed from a structural point of view using Dissipation Element (DE) analysis, which is a gradient trajec- tory (GT) based method for compartmentalizing turbulent fields into space filling sub-regions in which scalars behave monotonically. In the context of combustion, this property is important, as DEs locally and unambiguously indicate the maximum extent a diffusive transport dominated structure, such as a flame, can potentially occupy in a turbulent flow. First, DE analysis is applied to the mixture fraction field Z of a series of direct numerical simulations (DNS) of non-premixed jet flames. In a statistical investigation, it is shown that the normalized DE parameter statistics as well as the characteristic scalings of the respective mean quantities do not differ from non-reacting turbulent flows and are therefore unaffected by the heat release. Additionally, it is demonstrated that the scalar dissipation rate χ can be related to the gradient of the larger local flow topology as represented by the DE gradient g. The DE parameters are then used in the construction of a regime diagram for non-premixed combustion which is verified by the DNS results. Secondly, non-local effects in DNS of premixed combustion are investigated in a series of spatially evolving jet flames. DE analysis is applied to the temperature fields T which, contrary to Z, possess a chemical source term. The self-similarity of the normalized DE length distribution is retained, but the statistics of the scalar difference ∆T show a clear influence of the flame structure. In the consecutive GT based flame structure analysis, it is shown that the introduction of extremal points close to the flame front leads to a significant thickening of both the preheating and inner reaction zone. This effect is quantified and related to the turbulent burning velocity. Finally, the insights gained are used in combustion modelling. The scaling and self-similarity of the DE parameter statistics are used in a framework for the prediction of combustion regimes in non-premixed combustion. This framework is applied in the Reynolds averaged Navier-Stokes simulation of a passenger car diesel engine. Further, a novel model for the probability density function of Z is presented, which considers effects of laminar regions and external intermittency.
%F PUB:(DE-HGF)11 ; PUB:(DE-HGF)3
%9 Dissertation / PhD ThesisBook
%R 10.18154/RWTH-2021-01043
%U https://publications.rwth-aachen.de/record/811229