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Title:Simulacija turbulentnega toka s hibridnim LES/URANS turbulentnim modelom z uporabo metode robnih elementov
Authors:Kocutar, Primož (Author)
Škerget, Leopold (Mentor) More about this mentor... New window
Ravnik, Jure (Co-mentor)
Files:.pdf DOK_Kocutar_Primoz_2014.pdf (26,97 MB)
 
Language:Slovenian
Work type:Dissertation (m)
Typology:2.08 - Doctoral Dissertation
Organization:FS - Faculty of Mechanical Engineering
Abstract:V doktorski disertaciji se posvečamo razvoju hibridnega LES/URANS turbulentnega modela na osnovi metode robnih elementov (MRE) za simulacijo turbulentnega toka tekočine. Za izračun toka tekočine rešujemo sistem Navier-Stokesovih enačb zapisan v hitrostno-vrtinčni formulaciji. Sistem enačb je sestavljen iz enačb kinematike vrtinčnega polja na robu in hitrostnega polja v območju, enačbe kinetike vrtinčnosti polja, energijske enačbe, ter prenosne enačbe turbulentne kinetične energije za izračun turbulentnih modelov. Za enačbo kinematike smo uporabili nefizikalno časovno shemo. Uporabili smo spojen LES/URANS hibridni turbulentni model, kjer je vmesna površina med LES in URANS območje določena s fizikalno veličino, ter je dinamično določena tekom simulacije. Za preklopni kriterij med LES in URANS območjem smo uporabili Reynoldsovo število določeno s turbulentno kinetično energijo, ter Reynoldsovo število določeno s skupno turbulentno kinetično energijo. Glavna značilnost spojenih hibridnih modelov je, da za izračun toka uporabljajo en set vodilnih enačb. LES in URANS model sta v povezavi s preklopnim kriterijem spojena v prenosni enačbi turbulentne kinetične energije. V odvisnosti od karakteristike toka, ter preklopnega kriterija, za določeno območje uporabimo pod-mrežno ali URANS efektivno viskoznost. Pod-mrežna ali URANS viskoznost je nadaljnje uporabljena v prenosni enačbi turbulentne kinetične energije, ter v vodilnih enačbah za izračun toka tekočine. V hibridnem LES/URANS turbulentnem modelu je LES model uporabljen za vrtince z največ energije, torej velike vrtince, ter URANS model za obstensko območje. Za LES in URANS model smo uporabili modela, ki temeljita na turbulentni kinetični energiji, pri čemer smo za URANS model izbrali eno-enačbeni model razvit za obstenska območja. Numerični algoritem smo najprej validirali na testnih primerih. Za validacijo vodilnih enačb toka tekočine smo uporabili testni primer direktne numerične simulacije toka v gnani kotanji, ter za validacijo energijske enačbe direktno numerično simulacijo toka naravne konvekcije pri nižjih Rayleighevih številih. Po uspešni validaciji z uporabo direktne numerične simulacije, smo razvit LES/URANS hibridni turbulentni model testirali na turbulentnem toku naravne konvekcije v kvadratni kotanji, s čimer smo potrdili pravilnost delovanja hibridnega modela.
Keywords:metoda robnih elementov, hibridni LES-RANS model, prenos toplote, turbulentni tok, hitrostno vrtinčen zapis, računalniška dinamika tekočin, naravna konvekcija
Year of publishing:2014
Publisher:P. Kocutar]
Source:[Maribor
UDC:532.517.4-048.63:519.6(043.3)
COBISS_ID:276957440 Link is opened in a new window
NUK URN:URN:SI:UM:DK:0EZW5PN6
Views:1210
Downloads:114
Metadata:XML RDF-CHPDL DC-XML DC-RDF
Categories:KTFMB - FS
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Secondary language

Language:English
Title:Turbulent flow simulation using hybrid LES/URANS turbulent model by boundary element method
Abstract:Present PhD dissertation focuses on a hybrid LES/URANS turbulent model based on boundary element method (BEM) algorithm for turbulent fluid flow simulation. For fluid flow computation we solve the system of Navier-Stokes equations written in velocity-vorticity formulation. In system of equation we solve kinematic equation for boundary vorticity and domain velocity, kinetic equation for domain vorticity, energy equation and transport equation for turbulent kinetic energy for turbulent fluid flow computation. For kinematic equation we used false transient time scheme. We used unified LES/URANS hybrid turbulent model, where LES/URANS interface is dynamically defined with physical quantity during numerical simulation. For switching criterion between LES and URANS region we used Reynolds number based on turbulent kinetic energy and Reynolds number based on total turbulent kinetic energy. Unified hybrid models use one set of governing equations for fluid flow simulation. In present hybrid model, LES and URANS models are in connection with switching criterion joined in transport equation for turbulent kinetic energy. Effective viscosity, sub-grid or URANS, is used in transport equation for turbulent kinetic energy and in governing equations for fluid flow computation. With use of switching criterion we choose between sub-grid and URANS viscosity depending on fluid characteristics. The main idea of hybrid models is use of LES model for energy-contain vortexes in bulk flow and URANS model for near flow regions. Both LES and URANS model are based on turbulent kinetic energy. Used URANS model is one-equation model developed for near-wall regions. We validate numerical algorithm on benchmark tests. For fluid flow governing equations we used direct numerical simulation of driven cavity flow and for energy equation validation direct numerical simulation of natural convection flow at low Rayleigh numbers. Developed hybrid LES/URANS turbulent model was tested on turbulent natural convection flow in a square cavity.
Keywords:boundary element method, hybrid LES-RANS model, heat transfer, fluid flow, velocity-vorticity formulation, computational fluid dynamics, natural convection


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