TU Darmstadt / ULB / TUbiblio

A hybrid LES-CAA approach for the simulation and analysis of thermoacoustics in aero-engines

Reinhardt, Hanna (2024)
A hybrid LES-CAA approach for the simulation and analysis of thermoacoustics in aero-engines.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00026738
Ph.D. Thesis, Primary publication, Publisher's Version

Abstract

The collective global initiative to combat climate change has prompted aircraft manufacturers to adopt measures to reduce carbon emissions. One such measure involves the development of innovative combustor systems that use lean combustion modes to lower the emissions of pollutants such as NOx and CO2. However, this can result in fluctuations in mixing and heat-release rate, which can increase thermoacoustic activity, potentially affecting engine operation. Therefore, a comprehensive understanding of thermoacoustic phenomena is imperative for the effective and reliable design of large-scale combustion systems. Numerical simulations are often a helpful complement to experimental acoustic characterizations of industrial configurations. These methods usually use either fully compressible and resource-intensive Computational Fluid Dynamics (CFD) simulations, which naturally contain acoustic fluctuations in their computations, or two-step approaches that rely on source terms extracted from CFD simulations to supply subsequent Computational Aeroacoustics (CAA) simulations. However, compressible simulations can be costly depending on the configuration, and two-step approaches mostly do not include any two-way coupling between acoustics and the flow field. Hybrid methods simultaneously considering acoustics and fluid dynamics offer an elegant third option for numerically predicting combustion instabilities. In this thesis, a hybrid CFD-CAA framework for combustion noise investigations is extended to additionally enable an acoustic feedback on the flow, which allows for the description of thermoacoustic instabilities. The approach involves coupling acoustic and convective phenomena by deriving mean flow field quantities and acoustic sources from the low-Mach CFD solution and input them into the acoustic governing equations in the CAA solver. The resulting fluctuating acoustic quantities, namely pressure and velocity, are subsequently integrated into the solution of the low Mach number Navier-Stokes equations, where they affect the convective dynamics of the flow field, providing a closed feedback loop. This work addresses three main objectives in the development process of a novel numerical method. Firstly, the acoustic feedback mechanism is developed, implemented, and verified. Secondly, the thermoacoustic feedback cycle is verified by means of a generic configuration. Conventional compressible CFD simulations are used as reference. Thirdly, the approach is applied to an industry-relevant configuration. This configuration is an experimental test rig, providing experimental reference data for the thermoacoustic response of the considered system. For this validation step, both experimental and numerical reference data is used to assess the validity of the results obtained using the hybrid CFD-CAA approach.

Item Type: Ph.D. Thesis
Erschienen: 2024
Creators: Reinhardt, Hanna
Type of entry: Primary publication
Title: A hybrid LES-CAA approach for the simulation and analysis of thermoacoustics in aero-engines
Language: English
Referees: Hasse, Prof. Dr. Christian ; Janicka, Prof. Dr. Johannes
Date: 14 March 2024
Place of Publication: Darmstadt
Collation: xvi, 108, XVII Seiten
Refereed: 14 February 2024
DOI: 10.26083/tuprints-00026738
URL / URN: https://tuprints.ulb.tu-darmstadt.de/26738
Abstract:

The collective global initiative to combat climate change has prompted aircraft manufacturers to adopt measures to reduce carbon emissions. One such measure involves the development of innovative combustor systems that use lean combustion modes to lower the emissions of pollutants such as NOx and CO2. However, this can result in fluctuations in mixing and heat-release rate, which can increase thermoacoustic activity, potentially affecting engine operation. Therefore, a comprehensive understanding of thermoacoustic phenomena is imperative for the effective and reliable design of large-scale combustion systems. Numerical simulations are often a helpful complement to experimental acoustic characterizations of industrial configurations. These methods usually use either fully compressible and resource-intensive Computational Fluid Dynamics (CFD) simulations, which naturally contain acoustic fluctuations in their computations, or two-step approaches that rely on source terms extracted from CFD simulations to supply subsequent Computational Aeroacoustics (CAA) simulations. However, compressible simulations can be costly depending on the configuration, and two-step approaches mostly do not include any two-way coupling between acoustics and the flow field. Hybrid methods simultaneously considering acoustics and fluid dynamics offer an elegant third option for numerically predicting combustion instabilities. In this thesis, a hybrid CFD-CAA framework for combustion noise investigations is extended to additionally enable an acoustic feedback on the flow, which allows for the description of thermoacoustic instabilities. The approach involves coupling acoustic and convective phenomena by deriving mean flow field quantities and acoustic sources from the low-Mach CFD solution and input them into the acoustic governing equations in the CAA solver. The resulting fluctuating acoustic quantities, namely pressure and velocity, are subsequently integrated into the solution of the low Mach number Navier-Stokes equations, where they affect the convective dynamics of the flow field, providing a closed feedback loop. This work addresses three main objectives in the development process of a novel numerical method. Firstly, the acoustic feedback mechanism is developed, implemented, and verified. Secondly, the thermoacoustic feedback cycle is verified by means of a generic configuration. Conventional compressible CFD simulations are used as reference. Thirdly, the approach is applied to an industry-relevant configuration. This configuration is an experimental test rig, providing experimental reference data for the thermoacoustic response of the considered system. For this validation step, both experimental and numerical reference data is used to assess the validity of the results obtained using the hybrid CFD-CAA approach.

Alternative Abstract:
Alternative abstract Language

Gemeinsame globale Initiativen zur Bekämpfung des Klimawandels haben die Flugzeughersteller dazu veranlasst, Maßnahmen zur Verringerung der Treibhausgasemissionen zu ergreifen. Eine dieser Maßnahmen ist die Entwicklung innovativer Verbrennungssysteme, die durch magere Verbrennung den Ausstoß von Schadstoffen wie NOx und CO2 verringern. Dies kann jedoch zu Schwankungen bei der Gemischbildung und der Wärmefreisetzung führen, die die thermoakustische Aktivität erhöhen und den Triebwerksbetrieb beeinträchtigen können. Daher ist ein umfassendes Verständnis der thermoakustischen Phänomene für die wirksame und zuverlässige Auslegung von Verbrennungssystemen im großen Maßstab unabdingbar. Numerische Simulationen sind häufig eine nützliche Unterstützung bei der experimentellen akustischen Charakterisierung von Industrieanwendungen. Diese Methoden verwenden in der Regel entweder vollkompressible und rechenintensive CFD-Simulationen (Computational Fluid Dynamics), die naturgemäß akustische Fluktuationen enthalten, oder zweistufige Ansätze, die Quellterme aus CFD-Simulationen extrahieren, um nachfolgende CAA-Simulationen (Computational Aeroacoustics) zu unterstützen. Kompressible Simulationen können jedoch je nach Konfiguration sehr kostspielig sein, und bei zweistufigen Ansätzen gibt es meist keine wechselseitige Kopplung zwischen Akustik und Strömungsfeld. Hybride Methoden, die Akustik und Strömungsdynamik gleichzeitig berücksichtigen, bieten eine elegante dritte Option für die numerische Vorhersage von Verbrennungsinstabilitäten. In dieser Thesis wird ein CFD-CAA-Framework für Verbrennungslärmuntersuchungen erweitert, um eine akustische Rückkopplung auf die Strömung zu ermöglichen. Somit können auch thermoakustische Instabilitäten abgebildet werden. Der Ansatz beinhaltet die Kopplung von akustischen und konvektiven Phänomenen durch die Ableitung mittlerer Strömungsfeldgrößen und akustischer Quellen aus der Low-Mach-CFD-Lösung. Diese Größen werden in den akustischen Gleichungen im CAA-Löser verwendet. Die sich daraus ergebenden fluktuierenden akustischen Größen Druck und Schnelle werden anschließend in die Lösung der Navier-Stokes-Gleichungen für niedrige Machzahlen integriert, wo sie die konvektive Dynamik des Strömungsfeldes beeinflussen und eine geschlossene Feedback-Schleife bilden. Diese Arbeit verfolgt drei Hauptziele im Entwicklungsprozess einer neuartigen numerischen Methode. Erstens wird der akustische Feedback-Mechanismus entwickelt, implementiert und verifiziert. Zweitens wird der thermoakustische Feedback-Zyklus anhand einer generischen Konfiguration verifiziert. Konventionelle kompressible CFD-Simulationen werden als Referenz verwendet. Drittens wird der Ansatz auf eine industrierelevante Konfiguration angewendet. Diese Konfiguration ist ein experimenteller Prüfstand, der experimentelle Referenzdaten für die thermoakustische Antwort des betrachteten Systems liefert. In diesem Validierungsschritt werden sowohl experimentelle als auch numerische Referenzdaten verwendet, um die Validität der mit dem hybriden CFD-CAA-Ansatz erzielten Ergebnisse zu bewerten.

German
Status: Publisher's Version
URN: urn:nbn:de:tuda-tuprints-267384
Classification DDC: 600 Technology, medicine, applied sciences > 620 Engineering and machine engineering
Divisions: 16 Department of Mechanical Engineering
16 Department of Mechanical Engineering > Simulation of reactive Thermo-Fluid Systems (STFS)
Date Deposited: 14 Mar 2024 13:08
Last Modified: 15 Mar 2024 07:55
PPN:
Referees: Hasse, Prof. Dr. Christian ; Janicka, Prof. Dr. Johannes
Refereed / Verteidigung / mdl. Prüfung: 14 February 2024
Export:
Suche nach Titel in: TUfind oder in Google
Send an inquiry Send an inquiry

Options (only for editors)
Show editorial Details Show editorial Details