Title Numerically efficient modelling of turbulent non-premixed flames Title (croatian) Numerički efikasno modeliranje turbulentnih nepredmiješanih plamenova Author Mario Baburić Mentor Neven Duić (mentor)Committee member Željko Bogdan (predsjednik povjerenstva)Committee member Neven Duić (član povjerenstva)Committee member Antun Galović (član povjerenstva)Committee member Pedro Coelho (član povjerenstva) Committee member Reinhard Tatschl Granter University of Zagreb Defense date and country 2005-10-14, Croatia Scientific / art field, TECHNICAL SCIENCES Universal decimal classificationUDC ) 662 - Explosives. Fuels 51 - Mathematics Abstract A pre-tabulated chemistry approach, based on premixed and non-premixed laminar flamelets, was developed and implemented in this work. A devoted software application was developed in order to perform the chemistry calculations and tabulations in the preprocessor step. The combustion modelling in CFD procedure consisted of calculating the field distribution for a set of tracking scalars – mixture fraction and reaction progress variable – while the chemistry composition space was functionally related to these two scalars, depending on a model. The developed models were applied in the combustion simulations of three different configurations of varying complexity. The results were compared to experimental data and to the stationary laminar flamelet model predictions. The simulated configurations were following – a diluted hydrogen jet flame (H2/He-air flame B), a piloted methane jet flame (Sandia flame D) and a confined natural gas bluffbody stabilised flame (TECFLAM). Detailed chemical mechanisms were used in all cases. The discrete transfer radiation method was implemented into the CFD code (FIRE) in order to account for thermal radiation. The impact of radiation inclusion was investigated. A hybrid turbulence model was applied and its predictions were compared to those obtained with a standard k-ε model. A new tabulation procedure based on the normalised reaction progress variable has shown as a possible alternative to the standard stationary laminar flamelets methodology. In the case of premixed flamelets a complete range from the cold-mixing up to the chemical equilibrium can be covered, making this approach promising if searching towards more universal combustion models. NO was reasonably well predicted when using premixed flamelets, while non-premixed flamelets have shown as inappropriate in this particular situation. The reaction progress variable based models, as implemented in this work, have shown deficient in the fuel-rich regions in the methane jet configuration (Sandia flame D), making a space for possible improvements in this respect. The inclusion of radiation modelling has shown important for accurate temperature predictions. In general, the hybrid turbulence model has shown as superior to the standard k-ε turbulence model.
Abstract (croatian) Pristup tabeliranja kemijskih vrsta u pretprocesoru, baziran na izračunima predmiješanih
ili nepredmiješanih plamenova, je razvijen i implementiran u ovome radu. U tu svrhu je
razvijen računalni program u kojem se vrše proračuni kemijskih vrsta u pretprocesoru.
Modeliranje izgaranja tijekom same CFD procedure se sastoji u izračunu prostorne
raspodijeljenosti različitih skalara – udjela smjese goriva i varijable napretka reakcije –
dok su udjeli pojedinih kemijskih vrsta funkcionalno povezani sa ta dva skalara ovisno o
modelu. Razvijeni modeli su primijenjeni u proračunima izgaranja na tri konfiguracije s
različitim stupnjem složenosti. Rezultati simulacije su uspoređeni s eksperimentalno
dobivenim vrijednostima te s rezultatima simulacije dobivenih upotrebom standardnog
stacionarnog laminarnog flamelet modela. Simulirane konfiguracije su bile sljedeće –
prorijeđeni vodikov slobodni mlazni plamen (H2/He-zrak plamen B), pilotirani metanov
slobodni mlazni plamen (Sandia plamen D) te zatvoreni plamen prirodnog plina u
TECFLAM ložištu. U sva tri slučaja su upotrijebljeni detaljni kemijski mehanizmi.
Metoda diskretnog prijenosa topline zračenjem je implementirana u CFD program
(FIRE), a da bi se prilikom modeliranja obuhvatio proces prijenosa topline zračenjem.
Također, upotrebljen je hibridni model turbulencije prilikom modeliranja protoka fluida
te su njegovi rezultati uspoređeni s rezultatima dobivenim upotrebom standardnog k-ε
modela turbulencije.
Nova procedura tabeliranja kemijskih vrsta se pokazala kao mogućom alternativom
standardnom laminarnom flamelet modelu. U slučaju predmiješanih plamenova moguće
je obuhvatiti cjelokupno područje od hladnog miješanja reaktanata do ravnotežnog
izgaranja, što dopridonosi povećanoj univerzalnosti ovog modela. NO je dobro predviđen
modelom baziranom na predmiješanim plamenovima, dok se je upotreba nepredmiješanih
plamenova pokazala lošim izborom u ovome slučaju. Modeli bazirani na varijabli
napretka reakcije su se pokazali manjkavima u područjima s bogatom smjesom goriva u
slučaju Sandia plamena D te je potrebno ostvariti daljnji napredak u ovome pogledu.
Uključivanje modeliranja prijenosa topline zračenjem se pokazalo bitnim za točni izračun
temperaturnih polja. U općem slučaju, hibridni model turbulencije se pokazao boljim od
standardnog k-ε modela.
Keywords
non-premixed combustion
stationary laminar flamelet model
reaction progress variable
presumed conditional moments
chemistry pre-tabulation
diffusion flames
discrete transfer radiation method
hybrid turbulence model
Keywords (croatian)
Nepredmiješano izgaranje
stacionarni laminarni flamelet model
varijabla napretka reakcije
pretpostavljeni kondicionalni momenti
tabeliranje kemijskih vrsta
difuzijski plamenovi
metoda diskretnog prijenosa topline zračenjem
hibridni model turbulencije
Language english URN:NBN urn:nbn:hr:235:050072 Study programme Title: Mechanical Engineering and Naval Architecture Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2020-11-30 11:51:35
