Numerical modelling of turbulent premixed jet flames in large eddy simulation framework

doctoral thesis

• Title (croatian): Numeričko modeliranje turbulentnih predmiješanih plamenova metodom simulacije velikih vrtloga
• Author: Luka Perković
• Mentor: Neven Duić (mentor)
• Committee member: Željko Tuković (predsjednik povjerenstva)
• Committee member: Neven Duić (član povjerenstva)
• Committee member: Zdravko Virag (član povjerenstva)
• Committee member: Peter Priesching (član povjerenstva); strani drzavljanin: Nije dostupno
• Committee member: Franjo Juretić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2014-06-18, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; Process Energy Engineering
• Universal decimal classification (UDC): 621 - Mechanical engineering. Nuclear technology. Machinery ; 51 - Mathematics ; 004 - Computer science and technology. Computing. Data processing

Abstract

The main topic of this work's research is obtaining the methodological framework for large eddy simulation of turbulent premixed combustion. Obtaining this framework implies good knowledge of the state-of the-art in LES combustion, understanding the sub-grid scale (SGS) modelling of combustion and turbulent transport, proper definition of boundary conditions, quality mesh generation and proper numerical setup. In this work two different approaches have been used for SGS modelling of turbulent transport in Smagorinsky modelling framework. The first approach is the approach with constant value of Smagorinsky parameter. This approach is heavily relying on the chosen value of the parameter, which depends on flow configuration and simulation expertise and can introduce modelling errors if not chosen properly. Second approach is the Coherent Structure Method (CSM) approach, which is able to modify the Smagorinsky parameter according to the local coherence in the velocity field. Additionally, the CSM approach is in this work first-time used in the scope of the combustion modelling. The two approaches are mutually compared according to several criteria. The most significant comparison criteria is the comparison against available experimental data for two significantly different premixed combustion flames. The two approaches are also compared according to their level of numerical and discretization errors. Simulation results show that with the proposed methodological framework it is possible to get results which are comparable with experimental within approximately 20% of local discrepancy, with remark that CSM approach better reproduces fluctuations in the flow field. Furthermore, it is evaluated that probable cause of local discrepancy in validation comes from too excessive influence of combustion SGS modelling in regions of the flame front. This is directly related to insufficient resolution of the mesh resolution, even though the formal criteria of 80% of the resolved-to-total turbulent kinetic energy was satisfied. Conclusion is that the proposed methodological framework can be used for simulation of turbulent premixed combustion and that further improvement in result validation can be obtained by reducing the cell size in the flame region and further monitoring of numerical and discretization errors.

Abstract (croatian)

Tema ovog rada je dobivanje metodskog okvira za simulaciju turbulentnog predmiješanog plamena u okviru simulacije velikih vrtloga (eng. Large Eddy Simulation - LES). To podrazumijeva dobro poznavanje područja istraživanja vezanih uz područje simulacije velikih vrtloga, poput istraživanja vezanih uz pod-mrežne modele izgaranja i turbulentnog transporta, utjecaja definicije rubnih uvjeta kao i numeričkih postavki simulacije te utjecaj kvalitete i rezolucije računalne mreže. U ovome radu je dana usporedba dva različita pristupa računanja pod-mrežnog turbulentnog transporta u Smagorinsky-evom modelskom okviru, od kojih se jedan po prvi puta koristi za potrebe simuliranja izgaranja te su njegove implikacije na model izgaranja u ovome radu po prvi puta istražene. Prvi pristup je uobičajeni pristup u kojemu je modelski parametar Smagorinsky-evog model konstantan te ne ovisi o lokalnom toku već je uniforman u cijeloj domeni. Drugi pristup je metoda koherentnih struktura (eng. Coherent Structure Method - CSM), koji lokalno podešava parametar Smagorinsky-evog modela shodno lokalnoj koherentnosti u polju strujanja fluida. Dva pristupa su međusobno uspoređena prema nekoliko kriterija od kojih je najvažniji kriterij točnost rješenja usrednjenih i fluktuirajućih usporedbom s dostupnim eksperimentalnim podacima za dva značajno drugačija predmiješana plamena. Pristupi su također uspoređeni preko procjena grešaka diskretizacije te numeričkih grešaka. Rezultati pokazuju da je predloženim modelskim okvirima moguće dobiti zadovoljavajuća rješenja za značajno različite tipove plamena uz korištenje istih modelskih konstanti, uz napomenu da CSM pristup daje bolje rezultate fluktuirajućih veličina od pristupa sa uniformnim vrijednostima Smagorinsky-evog modelskog parametra. Nadalje, procjena je da najveći utjecaj na odstupanje od eksperimentalnih podataka uzrokuje preveliki utjecaj podmrežnog modela izgaranja, a koji je izravno vezan uz nedovoljnu rezoluciju mreže u području plamena iako je formalni kriterij od 80% izravnog rješenja u ukupnom zadovoljen za cijelu domenu. Zaključak je da predloženi modelski okvir može biti korišten u simulacijama predmiješanih turbulentnih plamenova te da se za daljnje povećanje razine točnosti rješenja predlaže korištenje finije mreže (u području plamena) od one koja je korištena u ovom radu.

• Keywords: premixed combustion; turbulence modelling; large eddy simulation; turbulence inflow procedure; non-reflective boundary conditions; coherent structure method; highly stretched flames; swirl flames
• Keywords (croatian): turbulentno predmiješano izgaranje; modeliranje turbulencije; metoda simulacije velikih vrtloga; turbulentni ulazni rubni uvjeti; ne-reflektivni rubni uvjeti; metoda koherentnih struktura; rastegnuti plamenovi; vrtložni plamenovi
• Language: english
• URN:NBN: urn:nbn:hr:235:777153
• Study programme: Title: Mechanical Engineering and Naval Architecture; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje tehničkih znanosti (doktor/doktorica znanosti, područje tehničkih znanosti)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2020-04-27 20:06:12