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1.
Heat-transfer characteristics of a non-newtonian Au nanofluid in a cubical enclosure with differentially heated side walls
Primož Ternik, Rebeka Rudolf, Zoran Žunič, 2015, izvirni znanstveni članek

Opis: The present work deals with the laminar natural convection in a cubical cavity filled with a homogenous aqueous solution of carboxymethyl cellulose (CMC) based gold (Au) nanofluid obeying the power-law rheological model. The cavity is heated on the vertical and cooled from the adjacent wall, while the other walls are adiabatic. The governing differential equations were solved with the standard finite-volume method and the hydrodynamic and thermal fields are coupled using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticle volume fraction on the heat-transfer characteristics of CMC-based Au nanofluid over a wide range of the base-fluid Rayleigh number. Accurate numerical results are presented in the form of dimensionless temperature and velocity variations, the mean Nusselt number and the heat-transfer rate. It is shown that adding nanoparticles to the base fluid delays the onset of natural convection. In addition, numerical simulations showed that, just after the onset of natural convection, adding nanoparticles reduces the mean Nusselt number value for any given base-fluid Rayleigh number.
Ključne besede: natural convection, CMC-Au nanofluid, heat transfer, Nusslet number
Objavljeno: 16.03.2017; Ogledov: 718; Prenosov: 69
.pdf Celotno besedilo (736,13 KB)
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2.
Siskov model toka nenewtonskih tekočin z metodo končnih prostornin
Marjan Delić, Jure Marn, Zoran Žunič, 2002, izvirni znanstveni članek

Opis: Analizirali smo primernost metode končnih prostornin za izračun tokovnih razmer v nestisljivi viskozni nenewtonski tekočini ob uporabi Siskovega modela. Prav tako smo analizirali natančnost numeričnih rezultatov v odvisnosti od gostote mreže. Metodo smo testirali na primeru gnanega toka v kotanji in primeru toka v kanalu z nenadno zožitvijo. Numerično dobljene rezultate smo primerjali z vrednostmi iz literature. Za reološki model smo uporabili modelne parametre, dobljene na podlagi preskusa s cevnim viskozimetrom.
Objavljeno: 10.07.2015; Ogledov: 604; Prenosov: 23
URL Povezava na celotno besedilo

3.
Tokovne razmere v avtomobilski lakirnici: numerična in eksperimentalna analiza
Jure Marn, Zoran Žunič, Matjaž Ramšak, Primož Ternik, 2002, izvirni znanstveni članek

Opis: V prispevku smo analizirali tokovne razmere v avtomobilski lakirni komori. Za reševanje Navier-Stokesovih enačb prostorskega toka nestisljive izotermne tekočine smo uporabili metodo nadzornih prostornin (CFX 5.4). Podrobno smo opisali potek izračuna, uporabljene robne in začetne pogoje, uporabljene metode za stabilizacijo numeričnih nihanj ter druge parametre, pomembne za izračun. Predstavili smo rezultate za ravninski in prostorski primer izračuna. Robni pogoji so bili določeni z meritvami na realni komori in to za primer brez avtomobila in z njim. Filter komore je bil upoštevan kot porozna snov s kvadratno funkcijo upora po podatkih proizvajalca, ki smo jih preverili z lastnimi meritvami padca tlakov.
Objavljeno: 10.07.2015; Ogledov: 569; Prenosov: 22
URL Povezava na celotno besedilo

4.
Numerical study of heat-transfer enhancement of homogeneous water-Au nanofluid under natural convection
Primož Ternik, Rebeka Rudolf, Zoran Žunič, 2012, izvirni znanstveni članek

Opis: A numerical analysis is performed to examine the heat transfer of colloidal dispersions of Au nanoparticles in water (Au nanofluids). The analysis used a two-dimensional enclosure under natural convection heat-transfer conditions and has been carried out for the Rayleigh number in the range of 103 < Ra < 105, and for the Au nanoparticles' volume-fraction range of 0 < j < 0.10. We report highly accurate numerical results indicating clearly that the mean Nusselt number is an increasing function of both Rayleigh number and volume fraction of Au nanoparticles. The results also indicate that a heat-transfer enhancement is possible using nanofluids in comparison to conventional fluids. However, low Rayleigh numbers show more enhancement compared to high Rayleigh numbers.
Ključne besede: natural convection, nanofluid, heat transfer, numerical modelling
Objavljeno: 10.07.2015; Ogledov: 778; Prenosov: 92
URL Povezava na celotno besedilo
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5.
Non-Newtonian blood flow around healthy and regurgitated aortic valve with coronary blood flow involved
Jure Marn, Jurij Iljaž, Zoran Žunič, Primož Ternik, 2012, izvirni znanstveni članek

Opis: Most numerical simulations about aortic valve are discussing about the blood flow through prosthetic valves, therefore this study covers a biological aortic valve. In this paper the simulation of blood flow around the regurgitated valve as well as around the health valve have been investigated and is showing how the regurgitation affects the heart function and coronary blood flow. Furthermore it also covers the coronary blood flow and its affect on the blood motion around the valve and consequently on the possible calcification. The physical problem has been treated for the period of closed valve, because of the regurgitation, which occurs at that time. For this restriction the assumption of non-elastic geometry has been used. Also the non-Newtonian Power Law model for the blood rheology has been used; because of the regions of slowly moving blood. Results are showing that the coronary blood flow does not have a high impact on the blood motion and thus the calcification is more probable as well that the regurgitation has a strong affect on the heart function, like aortic pressure drop, increased left ventricle volume, etc. The calcification reason has also been stated, but needs some further investigation. This paper covers in detail the geometry of computational domain and physics, so the results can be easily repeated.
Ključne besede: aortna zaklopka, regurgitacija, dinamika tekočin, nenewtonska tekočina
Objavljeno: 10.07.2015; Ogledov: 853; Prenosov: 83
URL Povezava na celotno besedilo

6.
Numerical study of Rayleigh-Bénard natural-convection heat-transfer characteristics of water-based Au nanofluids
Primož Ternik, Rebeka Rudolf, Zoran Žunič, 2013, izvirni znanstveni članek

Opis: The present work deals with the natural convection in a square cavity filled with a water-based Au nanofluid. The cavity is heated from the lower and cooled from the adjacent wall, while the other two walls are adiabatic. Theg overning differential equations have been solved with the standard finite volume method and the hydrodynamic and thermal fields have been coupled using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticlesć volume fraction on the heat-transfer characteristics of Au nanofluids at a given base-fluid (i.e., water) Rayleigh number Rabf. Accurate results are presented over a wide range of the base-fluid Rayleigh numbers (102 £ Rabf £ 105) and the volume fraction of Au nanoparticles (0 % £ j £ 10 %). It is shown that adding nanoparticles to the base fluid delays the onset of convection. Contrary to what is argued by many authors, we show, with numerical simulations, that the use of nanofluids can reduce the heat transfer instead of increasing it.
Ključne besede: Rayleigh-Bénard natural convection, water-Au nanofluid, heat transfer, numerical modelling
Objavljeno: 10.07.2015; Ogledov: 726; Prenosov: 81
.pdf Celotno besedilo (282,00 KB)
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7.
Vpliv biogoriv na tokovne pojave v vbrizgalni šobi dizelskega motorja
Blaž Vajda, 2013, doktorska disertacija

Opis: Vbrizgavanje curka goriva spada na področje dvofaznih tokov, ki obravnava karakteristike curka goriva v odvisnosti od fizikalnih lastnosti, s poudarkom na vbrizgavanju različnih goriv, pod različnimi delovnimi pogoji. Poleg ocene kvalitete tvorbe zmesi je raziskovanje karakteristik curka goriva pomembno tudi za oceno izkoriščenosti zraka v zgorevalni komori in zaradi morebitnega nezaželenega stika goriva s stenami zgorevalne komore. Obstoječi fizikalno-matematični modeli lahko v splošnem relativno natančno popišejo razmere dvofaznega toka. V samih podmodelih so prisotne empirične konstante (vplivni parametri), s pomočjo katerih se uravnavajo karakteristike vbrizganega curka in ki so v osnovi odvisne od lastnosti samega vbrizgalnega sistema, predvsem od geometrije vbrizgalne šobe. V okviru naloge bo vpeljan model, ki bo omogočal obravnavanje karakteristik različnih biogoriv, razmer v šobi in posledice vpliva karakteristik na razvoj, obliko in strukturo curka, kjer bo omogočeno natančnejše analiziranje dvofaznih tokov. Model bo zajemal prenosne enačbe za številsko gostoto parnih mehurčkov, z upoštevanjem fizikalnih procesov nastajanja in izginjanja posameznih mehurčkov, pri različnih oblikah kavitacijskih tokov, hkrati pa bo omogočal še raziskavo vpliva med kapljicami goriva ter obravnavo sil trka z vpeljavo velikostne porazdelitve kapljic goriva. Naloga je razdeljena na eksperimentalni in numerični del. V eksperimentalnem delu so določene in analizirane fizikalne lastnosti uporabljenih goriv, karakteristike procesa vbrizgavanja, s pomočjo hitre kamere pa je bil posnet razvoj curka goriva. V numeričnem delu je prikazan osnovni poenostavljeni fizikalno-matematični model. V disertaciji je pokazano, da je mogoče s spremembo fizikalno-matematičnega modela, ob upoštevanju fizikalnih lastnosti goriva, delovnega režima in karakteristik procesa vbrizgavanja, določiti konstante, ki pri izračunu uravnavajo karakteristike curka goriva. S pomočjo ustreznih izrazov je tako mogoče izraziti empirične vrednosti parametrov in vnaprej napovedati probleme, ki bi se lahko pojavili v dizelskih motorjih z uporabo biogoriv.
Ključne besede: alternativna goriva, sistem za vbrizgavanje goriva, tokovne razmere v šobi, kavitacija, curek goriva, računalniška dinamika tekočin.
Objavljeno: 12.07.2013; Ogledov: 1575; Prenosov: 188
.pdf Celotno besedilo (7,04 MB)

8.
Natural convection flows in complex cavities by BEM
Leopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2003, izvirni znanstveni članek

Opis: A numerical method for the solution of Navier-Stokes equations is developed using an integral representation of the conservation equations. The velocity- vorticity formulation is employed, where the kinematics is given with the Poisson equation for a velocity vector, while the kinetics is represented with the vorticity transport equation. The corresponding boundary-domain integral equations are presented along with discussions of the kinetics and kinematics of the fluid flow problem. THE BEM formulation is developed and tested for natural convection flows in closed cavities with complex geometries.
Ključne besede: fluid dynamics, natural convection, boundary element method, differential equations, closed cavity
Objavljeno: 01.06.2012; Ogledov: 1469; Prenosov: 69
URL Povezava na celotno besedilo

9.
Numerical simulation of dilute particle laden flows by wavelet BEM-FEM
Jure Ravnik, Leopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2008, izvirni znanstveni članek

Opis: A wavelet transform based BEM and FEM numerical scheme was used to simulate laminar viscous flow. The velocity-vorticity formulation of the Navier-Stokes equations was used. The flow simulation algorithm was coupled with a Lagrangian particle tracking scheme for dilute suspensions of massless particles and particles without inertia. The proposed numerical approach was used to simulate flow and particle paths for two test cases: flow over a backward-facing step and flow past a circular cylinder. We present methods of calculating the pressure and stream function field at the end of each time step. The pressure field was used to calculate drag and lift coefficients, which enable qualitative comparison of our results with the benchmark. The stream function enabled the comparison of streamlines and massless particle paths in steady state low Reynolds number value flow fields, and thus provided an estimate on the accuracy of the particle tracking algorithm. Unsteady higher Reynolds number value flows were investigated in terms of particle distributions in vortex streets in the wake of the cylinder and behind the step. Sedimentation of particles without inertia was studied in the flow field behind a backward-facing step at Reynolds number value 5000.
Ključne besede: boundary element method, velocity-vertocity formulation, discrete wavelet transform, Lagrangian particle tracking, backward-facing step, bluff body flow, dilute particle suspension
Objavljeno: 01.06.2012; Ogledov: 1345; Prenosov: 78
URL Povezava na celotno besedilo

10.
Combined single domain and subdomain BEM for 3D laminar viscous flow
Jure Ravnik, Leopold Škerget, Zoran Žunič, 2009, izvirni znanstveni članek

Opis: A subdomain boundary element method (BEM) using a continuous quadratic interpolation of function and discontinuous linear interpolation of flux is presented for the solution of the vorticity transport equation and the kinematics equation in 3D. By employing compatibility conditions between subdomains an over-determined system of linear equations is obtained, which is solved in a least squares manner. The method, combined with the single domain BEM, is used to solve laminar viscous flows using the velocity vorticity formulation of Navier-Stokes equations. The versatility and accuracy of the method are proven using the 3D lid driven cavity test case.
Ključne besede: subdomain boundary element method, laminar viscous fluid flow, velocity-vorticity fomulation, lid driven cavity
Objavljeno: 01.06.2012; Ogledov: 1290; Prenosov: 83
URL Povezava na celotno besedilo

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