Dietzsch, Felix (2018)
Tracking and analysis of flamelet structures in turbulent non-premixed combustion.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
In this thesis, two approaches to analyze flamelet structures in turbulent non-premixed combustion are presented. The analyses are based on a highly resolved direct numerical simulation (DNS) of a temporally evolving turbulent syngas jet flame that was conducted to this end. First, the simulation is analyzed by means of a novel on-the-fly tracking procedure to assess the model assumptions of a recently published extended flamelet formulation, which in contrast to the classical flamelet model, explicitly accounts for flame-tangential transport effects. After the extended model is modified to describe flamelets in a Lagrangian manner, flamelets are tracked in the DNS with the help of tracer particles that are attached to the iso-surface of stoichiometric mixture fraction. At each time step, gradient trajectories (flamelets) are emitted from these particles and are traced along the ascending and descending gradient until a local extremal point is reached. The on-the-fly tracking procedure thus allows a detailed analysis of single flamelets in turbulent flames and a full reconstruction of flamelet histories for the first time. In a second step, the history of flamelet identities is recomputed by means of a flamelet solver and a distinction is made between three different approaches (i) the classical flamelet (FLT), (ii) the curvature-affected flamelet (FLT-C) and (iii) the multi-dimensional flamelet (FLT-MD). Comparing the results of the recomputed histories with the DNS, it turns out that the FLT and FLT-C approaches mostly fail to reproduce the DNS results. On the other hand, the full extended FLT-MD approach agrees very well with the DNS for all identities considered, indicating that curvature-induced flame-tangential transport is an important aspect to consider in flamelet modeling. The study is complemented by a budget analysis of instantaneous flamelet identities, with which it is possible to quantify transient effects for the first time. The second approach analyzing flamelet structures consists in decomposing the mixture fraction field into small subunits called “dissipation elements”. Dissipation elements are defined as the ensemble of all gradient trajectories that end at the same local extremal points (minimum and maximum). However, in contrast to the on-the-fly tracking this procedure is applied during the postprocessing of the DNS and allows to identify all gradient trajectories. Originally developed for the statistical analysis of non-reacting flows, this methodology promotes novel flamelet-based modeling strategies. Classifying dissipation elements according to the location of their extremal points, statistics are computed and analyzed for two instants of time, considering the Euclidean distance l of the extremal points, the scalar difference ∆Z, the arithmetic mean Zm and an approximate gradient g = ∆Z/l . These statistics lead to further conclusions regarding the location of dissipation elements in mixture fraction space and how they are affected by turbulent mixing. Last, joint statistics of the temperature and the species mass fraction of OH with respect to g are inspected. It turns out, that there exists a strong correlation between the approximated gradient g and the quantities T and YOH, respectively.
Typ des Eintrags: | Dissertation | ||||
---|---|---|---|---|---|
Erschienen: | 2018 | ||||
Autor(en): | Dietzsch, Felix | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Tracking and analysis of flamelet structures in turbulent non-premixed combustion | ||||
Sprache: | Englisch | ||||
Referenten: | Hasse, Prof. Dr. Christian ; Thevenin, Prof. Dr. Dominique | ||||
Publikationsjahr: | 2018 | ||||
Ort: | Darmstadt | ||||
Datum der mündlichen Prüfung: | 10 Januar 2018 | ||||
URL / URN: | http://tuprints.ulb.tu-darmstadt.de/7218 | ||||
Kurzbeschreibung (Abstract): | In this thesis, two approaches to analyze flamelet structures in turbulent non-premixed combustion are presented. The analyses are based on a highly resolved direct numerical simulation (DNS) of a temporally evolving turbulent syngas jet flame that was conducted to this end. First, the simulation is analyzed by means of a novel on-the-fly tracking procedure to assess the model assumptions of a recently published extended flamelet formulation, which in contrast to the classical flamelet model, explicitly accounts for flame-tangential transport effects. After the extended model is modified to describe flamelets in a Lagrangian manner, flamelets are tracked in the DNS with the help of tracer particles that are attached to the iso-surface of stoichiometric mixture fraction. At each time step, gradient trajectories (flamelets) are emitted from these particles and are traced along the ascending and descending gradient until a local extremal point is reached. The on-the-fly tracking procedure thus allows a detailed analysis of single flamelets in turbulent flames and a full reconstruction of flamelet histories for the first time. In a second step, the history of flamelet identities is recomputed by means of a flamelet solver and a distinction is made between three different approaches (i) the classical flamelet (FLT), (ii) the curvature-affected flamelet (FLT-C) and (iii) the multi-dimensional flamelet (FLT-MD). Comparing the results of the recomputed histories with the DNS, it turns out that the FLT and FLT-C approaches mostly fail to reproduce the DNS results. On the other hand, the full extended FLT-MD approach agrees very well with the DNS for all identities considered, indicating that curvature-induced flame-tangential transport is an important aspect to consider in flamelet modeling. The study is complemented by a budget analysis of instantaneous flamelet identities, with which it is possible to quantify transient effects for the first time. The second approach analyzing flamelet structures consists in decomposing the mixture fraction field into small subunits called “dissipation elements”. Dissipation elements are defined as the ensemble of all gradient trajectories that end at the same local extremal points (minimum and maximum). However, in contrast to the on-the-fly tracking this procedure is applied during the postprocessing of the DNS and allows to identify all gradient trajectories. Originally developed for the statistical analysis of non-reacting flows, this methodology promotes novel flamelet-based modeling strategies. Classifying dissipation elements according to the location of their extremal points, statistics are computed and analyzed for two instants of time, considering the Euclidean distance l of the extremal points, the scalar difference ∆Z, the arithmetic mean Zm and an approximate gradient g = ∆Z/l . These statistics lead to further conclusions regarding the location of dissipation elements in mixture fraction space and how they are affected by turbulent mixing. Last, joint statistics of the temperature and the species mass fraction of OH with respect to g are inspected. It turns out, that there exists a strong correlation between the approximated gradient g and the quantities T and YOH, respectively. |
||||
Alternatives oder übersetztes Abstract: |
|
||||
URN: | urn:nbn:de:tuda-tuprints-72189 | ||||
Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau | ||||
Fachbereich(e)/-gebiet(e): | 16 Fachbereich Maschinenbau > Fachgebiet Simulation reaktiver Thermo-Fluid Systeme (STFS) 16 Fachbereich Maschinenbau |
||||
Hinterlegungsdatum: | 18 Feb 2018 20:55 | ||||
Letzte Änderung: | 18 Feb 2018 20:55 | ||||
PPN: | |||||
Referenten: | Hasse, Prof. Dr. Christian ; Thevenin, Prof. Dr. Dominique | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 10 Januar 2018 | ||||
Export: | |||||
Suche nach Titel in: | TUfind oder in Google |
Frage zum Eintrag |
Optionen (nur für Redakteure)
Redaktionelle Details anzeigen |