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Eulerian-lagrangian approach for modeling and simulations of turbulent reactive multi-phase flows under gas turbine combustor conditions

Chrigui, Mouldi (2005)
Eulerian-lagrangian approach for modeling and simulations of turbulent reactive multi-phase flows under gas turbine combustor conditions.
Technische Universität Darmstadt
Ph.D. Thesis, Primary publication

Abstract

The work presented in this thesis resulted in the development and application of different mathematical sub-models to describe the physics of turbulent reacting spray typical for gas turbine combustors. The resulting complete models were formulated in the Eulerian-Lagrangian context. Emphases were primarily put on the interaction between solid particles and turbulence seeking a correct prediction of turbulent quantities in turbulent two phase flows. The investigation of the feedback mechanism of particles on the continuous phase within the turbulent two-phase flow which is known as turbulence modulation was carried out with three different modulation models. Computations reveal that the obtained results of the turbulent kinetic energy using the thermodynamically consistent model, reproduce well both the turbulence attenuation and production. Indeed, the standard model underestimates the turbulence. This model is dissipative for small and big particles, whereas the model by Crowe is overall productive. Two evaporation models have been developed, integrated in FASTEST/LAG3D code and subsequently applied. The computations were achieved using a fully two-way coupling process. A systematical study of the interaction processes including turbulence, turbulence modulation, mass and heat transfer has been satisfactory carried out. Simulations showed that non equilibrium model agree most favorably with experimental measurements of the droplet mass flux. In order to characterize the turbulence-droplet vaporization interaction regimes, a vaporization Damkoehler number (Dav) has been introduced. Numerical results have demonstrated that in case of Dav>1 turbulence augmentation enhances the evaporation rate, whereas for Dav¡Ü1 the opposite phenomenon takes place, namely the rate of evaporation is reduced. The spray combustion was studied in a complex industrial configuration, which consists of a single annular combustor that was experimentally measured by Rolls-Royce Deutschland. Simulations were performed using k-eps as well as Reynolds Stress model (Jones Musonge) for turbulence, an assumed shape of probability density function to prescribe turbulence combustion interaction and different models describing the turbulence modulation. Equilibrium and a flamelet chemistry approaches were used. Results showed that predicted RTDF distributions are satisfactory and provide plausible results compared with measurements. The use of the thermodynamically consistent modulation model allows an acceptable behavior of the temperature distribution compared to the standard modulation model. On the other hand, both evaporation models (equilibrium and non-equilibrium) provided similar results for the temperature distribution. Numerical computations including the flamelet turbulent combustion model predicted a lower peak reaction temperature and a more gradual temperature decrease than predictions using equilibrium chemistry. As final conclusion one can reiterate that the combination of the following sub-models: thermodynamically consistent model for the turbulence modulation, Langmuir-Knudsen non-equilibrium model for the evaporation, Reynolds Stress Model for the turbulence and flamelet model for the chemistry establish a reliable complete model that seems to allows a better description of reactive multi-phase flow studied in the frame of this work.

Item Type: Ph.D. Thesis
Erschienen: 2005
Creators: Chrigui, Mouldi
Type of entry: Primary publication
Title: Eulerian-lagrangian approach for modeling and simulations of turbulent reactive multi-phase flows under gas turbine combustor conditions
Language: English
Referees: Bauer, Prof. Dr.- Hans-Jörg ; Sadiki, Prof. Dr. Amsini
Advisors: Janicka, Prof. Dr.- Johannes
Date: 16 December 2005
Place of Publication: Darmstadt
Publisher: Technische Universität
Collation: X, 160 S. : graph.Darst.
Refereed: 23 November 2005
URL / URN: urn:nbn:de:tuda-tuprints-6358
Abstract:

The work presented in this thesis resulted in the development and application of different mathematical sub-models to describe the physics of turbulent reacting spray typical for gas turbine combustors. The resulting complete models were formulated in the Eulerian-Lagrangian context. Emphases were primarily put on the interaction between solid particles and turbulence seeking a correct prediction of turbulent quantities in turbulent two phase flows. The investigation of the feedback mechanism of particles on the continuous phase within the turbulent two-phase flow which is known as turbulence modulation was carried out with three different modulation models. Computations reveal that the obtained results of the turbulent kinetic energy using the thermodynamically consistent model, reproduce well both the turbulence attenuation and production. Indeed, the standard model underestimates the turbulence. This model is dissipative for small and big particles, whereas the model by Crowe is overall productive. Two evaporation models have been developed, integrated in FASTEST/LAG3D code and subsequently applied. The computations were achieved using a fully two-way coupling process. A systematical study of the interaction processes including turbulence, turbulence modulation, mass and heat transfer has been satisfactory carried out. Simulations showed that non equilibrium model agree most favorably with experimental measurements of the droplet mass flux. In order to characterize the turbulence-droplet vaporization interaction regimes, a vaporization Damkoehler number (Dav) has been introduced. Numerical results have demonstrated that in case of Dav>1 turbulence augmentation enhances the evaporation rate, whereas for Dav¡Ü1 the opposite phenomenon takes place, namely the rate of evaporation is reduced. The spray combustion was studied in a complex industrial configuration, which consists of a single annular combustor that was experimentally measured by Rolls-Royce Deutschland. Simulations were performed using k-eps as well as Reynolds Stress model (Jones Musonge) for turbulence, an assumed shape of probability density function to prescribe turbulence combustion interaction and different models describing the turbulence modulation. Equilibrium and a flamelet chemistry approaches were used. Results showed that predicted RTDF distributions are satisfactory and provide plausible results compared with measurements. The use of the thermodynamically consistent modulation model allows an acceptable behavior of the temperature distribution compared to the standard modulation model. On the other hand, both evaporation models (equilibrium and non-equilibrium) provided similar results for the temperature distribution. Numerical computations including the flamelet turbulent combustion model predicted a lower peak reaction temperature and a more gradual temperature decrease than predictions using equilibrium chemistry. As final conclusion one can reiterate that the combination of the following sub-models: thermodynamically consistent model for the turbulence modulation, Langmuir-Knudsen non-equilibrium model for the evaporation, Reynolds Stress Model for the turbulence and flamelet model for the chemistry establish a reliable complete model that seems to allows a better description of reactive multi-phase flow studied in the frame of this work.

Alternative Abstract:
Alternative abstract Language

Die angefertigte Arbeit befasst sich mit der Entwicklung und Validierung numerischer Berechnungsverfahren f¨¹r reagierende und nicht reagierende Mehrphasenströmungen auf dem Gebiet der Strömungs- und Verbrennungstechnik. Im Rahmen der Verwendung des Euler-Lagrange-Verfahrens wurde ein integrales Modul f¨¹r die Sprayverbrennung, bestehend aus mehreren Submodellen angewendet. Die Berechnung der kontinuierlichen Phase wurde hierbei mit der Methode der „Reynolds Averaging Numerical Simulation¡° (RANS) durchgef¨¹hrt. Die disperse Phase wurde im Rahmen des Lagrangeschen Ansatzes als Partikeln im Strömungsfeld verfolgt. Aus der Berechnung einer Vielzahl von Partikeltrajektorien im Strömungsgebiet wurden durch eine geeignete Ensemblemittelung sowohl Partikelkenngrößen, als auch Phasenwechselwirkungsterme f¨¹r die Impuls-, Masse-, Wärme-, und Mischungsbruch¨¹bertragung abgeleitet. Drei Ansätze zur Beschreibung der Turbulenzmodulation wurden untersucht. Das Standard-Modulationsmodell zeigte ein dissipatives Verhalten f¨¹r kleine als auch große Partikel. Das Modell von Crowe, welches auf der Energiebilanz basiert, produzierte verglichen mit experimentellen Messungen zu hohe Werte der turbulenten kinetischen Energie. Das thermodynamisch konsistente Modell war in der Lage, sowohl Produktion als auch Dissipation der von den Partikeln induzierten Turbulenz abzubilden. Zur Ber¨¹cksichtigung der Phasen¨¹bergangsphänomene wurden zwei Verdampfungs-modelle in das Spraymodul integriert und validiert. Das erste Modell basiert auf dem „Uniform Temperature¡° -Ansatz, in dessen Rahmen die Bestimmung des Massenbruchs auf der Tropfenoberfläche mit Hilfe der Gleichgewichtsannahme berechnet wird. Das zweite Verdampfungsmodell (Langmuir & Knudsen) ber¨¹cksichtigt die Nichtgleichgewichtseffekte durch die Berechnung eines Abweichungsparameters, der von den thermodynamischen Größen (Druck, Temperatur, Viskosität etc.) abhängt. Die numerische Simulation hat gezeigt, dass das Gleichgewichtsverdampfungsmodell eine geringere Verdampfungsrate gegen¨¹ber den experimentellen Daten vorhersagt. Das Nichtgleichgewichtsmodell liefert dagegen eine sehr gute Übereinstimmung der Verdampfungsrate sowie der Verteilung des Tropfen-Massenflusses mit den experimentellen Daten in allen Messebenen. Durch eine Parameterstudie wurden die Effekte der Variation der Turbulenzintensität auf die Verdampfung untersucht. Interessante Ergebnisse haben uns dazu gef¨¹hrt, eine Verdampfungskenngröße zu definieren, um Interaktionregime charakterisieren zu können. Die Konfiguration, welche von Rolls Royce Deutschland experimentell untersucht wurde, beschreibt eine Sprayverdampfung und -verbrennung in einer komplexen Industriebrennkammer einer Gasturbine. Das integrale Sprayverbrennungsmodul wurde angewendet und die Einfl¨¹sse der Turbulenzmodulation, Verdampfungseffekte, Gleichgewichts- sowie Flamelet-Chemie wurden studiert. Die numerischen Ergebnisse der Temperaturprofile wurden mit Messungen am Brennkammeraustritt verglichen. Die berechneten Profile des „Radial Temperature Distribution Factor¡° haben eine gute Übereinstimmung wiedergegeben. Die numerischen Untersuchungen haben gezeigt, dass ein optimales integrales Sprayverbrennungsmodul sich aus folgenden Submodellen zusammensetzt: Das thermodynamisch konsistente Modulationsmodell zur Ber¨¹cksichtigung der Turbulenzänderung, das Nichtgleichgewichtsverdampfungsmodell f¨¹r die Phasenänderung, Reynolds-Stress-Modell zur Beschreibung der Turbulenz, Flamelet f¨¹r die Chemieerfassung und die Presumed-PDF zur Beschreibung der Chemie-Turbulenzwechselwirkung.

German
Uncontrolled Keywords: Zweiphasen, Mehrphasen, Strömung, Euler-Lagrange-Verfahren
Alternative keywords:
Alternative keywordsLanguage
multiphase, two-phase, dispersion, modulation, turbulence, evaporation, flame, combustionEnglish
Classification DDC: 600 Technology, medicine, applied sciences > 620 Engineering and machine engineering
Divisions: 16 Department of Mechanical Engineering
Date Deposited: 20 Nov 2008 08:22
Last Modified: 10 Apr 2019 11:34
PPN:
Referees: Bauer, Prof. Dr.- Hans-Jörg ; Sadiki, Prof. Dr. Amsini
Refereed / Verteidigung / mdl. Prüfung: 23 November 2005
Alternative keywords:
Alternative keywordsLanguage
multiphase, two-phase, dispersion, modulation, turbulence, evaporation, flame, combustionEnglish
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