Computational fluid dynamics simulations of thermal flows in various applications

Alpo Laitinen

Computational fluid dynamics simulations of thermal flows in various applications

Julkaisun otsikon käännös: Laskennallisia virtausdynamiikan simulaatioita termisistä virtauksista moninaisissa sovelluksissa

Alpo Laitinen

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Tämä väitöskirja kuuluu laskennallisen fysiikan aihepiiriin. Eritoten, laskennallisen virtausdynamiikan (computational ﬂ uid dynamics) metodeja käytetään simuloimaan lämmönsiirron ja ﬂ uidivirtausten ilmiöitä, metodologinen painopiste suurten pyörteiden menetelmän (large eddy simulation) käyttämisessä. Työn yleinen tarkoitus on käyttää LES:iä moninaisissa yhteiskunnallisesti merkityksellisissä sovelluksissa eri mittakaavoissa. Tämäväitöskirja on yksi uraauurtavista töistä LES:n käytöstä konjugaattilämmönsiirrossa, soodakattilassa ja sisäilmavirtauksessa. Julkaisussa I suunniteltiin ja numeerisesti analysoitiin virtauskanavia sisältävä nestejäähdytyslämmönvaihdin tehokkaan elektroniikan jäähdyttämistä varten. Julkaisussa on raportoitu myös tekijöiden tekemiä kokeita lämmönvaihtimen toimivuuden vahvistamiseksi. Numeerinen analyysi suoritettiin kolmella eri turbulenssimallilla, ja vertailu paljasti merkittäviä eroja lämmönsiirtokyvyssä olennaisten virtausominaisuuksien tunnistamisen perusteella.Erityisesti turbulenssitason yliarvioinnin havaittiin myös yliarvioivan turbulenttia lämmönsiirtoa ja siten aliarvioivan pinnan lämpötilatasoja. Julkaisussa II analysoitiin LES:llä soodakattila, jossa oli kaksi erilaista ilmasuihkukonﬁguraatiota. Virtauskentän lisäksi mustalipeäpisaroiden dispersiota simuloitiin kiinteinä hiukkasina Lagrangen hiukkasseurannalla (lagrangian particle tracking). Kahdessa suihkukonﬁ guraatiossa oli erojakuuman ja kylmän kaasun sekoituksessa sekä hiukkasten leviämisessä. Porrastettu suihkukonﬁ guraatio tarjosi tasaisemmat lämpötilatasot verrattuna vastakkain asteltuihin suihkuihin. Porrastetussa konﬁ guraatiossa havaittiin kuitenkin huomattavasti enemmän likaantumista. Julkaisussa III suuri huone, jossa oli koneellinen ilmanvaihto, simuloitiin käyttämällä LES:ää. Simulaatiotapauksen motiivina oli tosielämän SARS-CoV-2-viruksen superleviämistapahtuma kuoroharjoituksen aikana. Simulaation painopisteenä olivat lämmityspatterien ja kuoroon osallistuvien synnyttämät lämpöpluumit sekä nosteen vaikutus hengitysaerosolien leviämiseen. Nosteen havaittiin lisäävän hengitysaerosolien turbulenttia leviämistä merkittävästi. Popen kriteeriä käytettiin numeerisen ratkaisun veriﬁ oinniksi julkaisuissa II ja III. Yhteenvetona voidaan todeta, että mittakaavat ratkaisevien tekniikoiden (esim. LES) käyttö vaikuttaa tärkeältä simuloidessa virtauksia, joilla on turbulenssisiirtymäominaisuuksia, ja tuottavat voimakkaastiturbulenssia mikä vaikuttaa esimerkiksi hiukkasten leviämiskuvioihin tai seinämän lämmönsiirtoon.

Julkaisun otsikon käännös	Laskennallisia virtausdynamiikan simulaatioita termisistä virtauksista moninaisissa sovelluksissa
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Vuorinen, Ville, Vastuuprofessori Vuorinen, Ville, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-64-1382-2
Sähköinen ISBN	978-952-64-1383-9
Tila	Julkaistu - 2023
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

turbulenssi
lämmönsiirto
laskennallinen virtausdynamiikka
suurten pyörteiden metodi

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-64-1383-9

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@phdthesis{1c7cbd7b54b4449582ee20afe593014f,

title = "Computational fluid dynamics simulations of thermal flows in various applications",

abstract = "The present thesis belongs to the field of computational physics. In particular, computational fluid dynamics (CFD) methods are utilized to simulate heat transfer and fluid flow phenomena, with the methodological emphasis on using scale-resolving large-eddy simulations (LES). The overall objective of the thesis is to utilize LES in various societally relevant applications on various scales. The dissertation is among pioneering works on the usage of LES in conjugate heat transfer, recovery boiler, and indoor airflow context. In Publication I, a liquid cooling heat exchanger with embedded channels for high power electronics was designed and numerically analyzed. Experiments carried by co-authors are also reported in the publication to confirm the functionality of the heat exchanger. The numerical analysis was performed with three different turbulence models, and the comparison revealed significant differences in the thermal performance based on the capturing of the relevant flow features. In particular, the overprediction in the level of turbulence was observed to also overpredict the turbulent heat transfer and consequently, underpredict the surface temperature levels. In Publication II, a kraft recovery boiler with two different secondary air jet configurations was analyzed with LES. In addition to the flow field, dispersion of black liquor droplets was simulated as solid particles with Lagrangian particle tracking (LPT). The two jet configurations exhibited differences in the mixing of the hot and cool gases as well as in the dispersion of the particles. A staggered jet configuration provided more uniform temperature levels compared to an in-line configuration. However, significantly more fouling was observed in the staggered configuration. In Publication III, a large room with mechanical ventilation was simulated using LES. The simulation case was motivated by a real life SARS-CoV-2 virus super-spreading event during a choir practice. The emphasis of the simulation was on the buoyancy-driven flows generated by the radiators and the choir attendees, and the effect of buoyancy on the dispersion of the respiratory aerosols. The presence of buoyancy was noted to increase the turbulent dispersion of the respiratory aerosols significantly. Pope's criterion was utilized to verify the numerical solution in Publication II and III. As an overall conclusion, usage of scale-resolving techniques (e.g. LES) appears important in predicting flows with transitional features and strong turbulence generation affecting e.g particle dispersion patterns or wall heat transfer.",

keywords = "turbulence, heat transfer, computational fluid dynamics, large-eddy simulation, turbulenssi, l{\"a}mm{\"o}nsiirto, laskennallinen virtausdynamiikka, suurten py{\"o}rteiden metodi, turbulence, heat transfer, computational fluid dynamics, large-eddy simulation",

author = "Alpo Laitinen",

year = "2023",

language = "English",

isbn = "978-952-64-1382-2",

series = "Aalto University publication series DOCTORAL THESES",

publisher = "Aalto University",

number = "124",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Computational fluid dynamics simulations of thermal flows in various applications

AU - Laitinen, Alpo

PY - 2023

Y1 - 2023

N2 - The present thesis belongs to the field of computational physics. In particular, computational fluid dynamics (CFD) methods are utilized to simulate heat transfer and fluid flow phenomena, with the methodological emphasis on using scale-resolving large-eddy simulations (LES). The overall objective of the thesis is to utilize LES in various societally relevant applications on various scales. The dissertation is among pioneering works on the usage of LES in conjugate heat transfer, recovery boiler, and indoor airflow context. In Publication I, a liquid cooling heat exchanger with embedded channels for high power electronics was designed and numerically analyzed. Experiments carried by co-authors are also reported in the publication to confirm the functionality of the heat exchanger. The numerical analysis was performed with three different turbulence models, and the comparison revealed significant differences in the thermal performance based on the capturing of the relevant flow features. In particular, the overprediction in the level of turbulence was observed to also overpredict the turbulent heat transfer and consequently, underpredict the surface temperature levels. In Publication II, a kraft recovery boiler with two different secondary air jet configurations was analyzed with LES. In addition to the flow field, dispersion of black liquor droplets was simulated as solid particles with Lagrangian particle tracking (LPT). The two jet configurations exhibited differences in the mixing of the hot and cool gases as well as in the dispersion of the particles. A staggered jet configuration provided more uniform temperature levels compared to an in-line configuration. However, significantly more fouling was observed in the staggered configuration. In Publication III, a large room with mechanical ventilation was simulated using LES. The simulation case was motivated by a real life SARS-CoV-2 virus super-spreading event during a choir practice. The emphasis of the simulation was on the buoyancy-driven flows generated by the radiators and the choir attendees, and the effect of buoyancy on the dispersion of the respiratory aerosols. The presence of buoyancy was noted to increase the turbulent dispersion of the respiratory aerosols significantly. Pope's criterion was utilized to verify the numerical solution in Publication II and III. As an overall conclusion, usage of scale-resolving techniques (e.g. LES) appears important in predicting flows with transitional features and strong turbulence generation affecting e.g particle dispersion patterns or wall heat transfer.

AB - The present thesis belongs to the field of computational physics. In particular, computational fluid dynamics (CFD) methods are utilized to simulate heat transfer and fluid flow phenomena, with the methodological emphasis on using scale-resolving large-eddy simulations (LES). The overall objective of the thesis is to utilize LES in various societally relevant applications on various scales. The dissertation is among pioneering works on the usage of LES in conjugate heat transfer, recovery boiler, and indoor airflow context. In Publication I, a liquid cooling heat exchanger with embedded channels for high power electronics was designed and numerically analyzed. Experiments carried by co-authors are also reported in the publication to confirm the functionality of the heat exchanger. The numerical analysis was performed with three different turbulence models, and the comparison revealed significant differences in the thermal performance based on the capturing of the relevant flow features. In particular, the overprediction in the level of turbulence was observed to also overpredict the turbulent heat transfer and consequently, underpredict the surface temperature levels. In Publication II, a kraft recovery boiler with two different secondary air jet configurations was analyzed with LES. In addition to the flow field, dispersion of black liquor droplets was simulated as solid particles with Lagrangian particle tracking (LPT). The two jet configurations exhibited differences in the mixing of the hot and cool gases as well as in the dispersion of the particles. A staggered jet configuration provided more uniform temperature levels compared to an in-line configuration. However, significantly more fouling was observed in the staggered configuration. In Publication III, a large room with mechanical ventilation was simulated using LES. The simulation case was motivated by a real life SARS-CoV-2 virus super-spreading event during a choir practice. The emphasis of the simulation was on the buoyancy-driven flows generated by the radiators and the choir attendees, and the effect of buoyancy on the dispersion of the respiratory aerosols. The presence of buoyancy was noted to increase the turbulent dispersion of the respiratory aerosols significantly. Pope's criterion was utilized to verify the numerical solution in Publication II and III. As an overall conclusion, usage of scale-resolving techniques (e.g. LES) appears important in predicting flows with transitional features and strong turbulence generation affecting e.g particle dispersion patterns or wall heat transfer.

KW - turbulence

KW - heat transfer

KW - computational fluid dynamics

KW - large-eddy simulation

KW - turbulenssi

KW - lämmönsiirto

KW - laskennallinen virtausdynamiikka

KW - suurten pyörteiden metodi

KW - turbulence

KW - heat transfer

KW - computational fluid dynamics

KW - large-eddy simulation

M3 - Doctoral Thesis

SN - 978-952-64-1382-2

T3 - Aalto University publication series DOCTORAL THESES

PB - Aalto University

ER -

Computational fluid dynamics simulations of thermal flows in various applications

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

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