31. Lagrangian particle tracking in velocity-vorticity resolved viscous flows by subdomain BEMJure Ravnik, Matjaž Hriberšek, Janez Lupše, 2016, original scientific article Abstract: A numerical study of particle motion in a cubic lid driven cavity is presented. As a computational tool, a boundary element based flow solver with a Lagrangian particle tracking algorithm is derived. Flow simulations were performed using an in-house boundary element based 3D viscous flow solver. The Lagrangian particle tracking algorithm is capable of simulation of dilute suspensions of particles in viscous flows taking into account gravity, buoyancy, drag, pressure gradient and added mass. The derived algorithm is used to simulate particle behaviour in a cellular flow field and in a lid driven cavity flow. Simulations of particle movement in a cellular flow field were used to validate the algorithm. The main goal of the paper was to numerically simulate the flow behaviour of spheres of different densities and different diameters, as experimentally observed in work of Tsorng et al.The study of slightly buoyant and non-buoyant particles in a lid driven cavity was aimed at discovering cases when particles leave the primary vortex and enter into secondary vortices, a phenomenon described in the work of Tsorng et al. A parametric study of this phenomenon was preformed. The presented computational results show excellent agreement with experiments, confirming the accuracy of the developed computational method.
Keywords: dispersed two phase flow, Lagrangian particle tracking, cellular flow, lid driven cavity, boundary element method
Published in DKUM: 04.08.2017; Views: 1279; Downloads: 414
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32. Analysis of the effect of the swirl flow intensity on combustion characteristics in liquid fuel powered confined swirling flamesMarko Klančišar, Tim Schloen, Matjaž Hriberšek, Niko Samec, 2016, original scientific article Abstract: This article examines the implementation of CFD technology in the design of the industrial liquid fuel powered swirl flame burner. The coupling between the flow field and the combustion model is based on the eddy dissipation model. The choice of the LES (Large Eddy Simulation) turbulence model over standard RANS (Reynolds Averaged Navier-Stokes) offers a possibility to improve the quality of the combustion-flow field interaction. The Wall Adapting Local Eddy-Viscosity (WALE) sub-grid model was used. The reaction chemistry is a simple infinitely fast one step global irreversible reaction. The computational model was setup with the Ansys-CFX software. Through the detailed measurements of industrial size burner, it was possible to determine the natural operational state of the burner according to the type of fuel used. For the inlet conditions, axial and radial velocity components were calculated from known physical characteristics of both the fuel and air input, with the initial tangential velocity of the fuel assumed as 18% of the initial axial fuel velocity. Different swirl number (S) values were studied. Addition of a surplus (in comparison to conventional flame stabilization) of tangential air velocity component (W), the rotational component increases itself with a considerably high magnitude, contributing to the overall flame stabilization. The level of S especially influences the turbulent energy, its dissipation rate and turbulent (Reynolds) stresses. In the case of high swirl number values (S > 0,65) it is possible to divide the flow field in three principle areas: mixing area (fuel-air), where exothermal reactions are taking place, central recirculation area and outer recirculation area, which primarily contains the flow of burnt flue gases. The described model was used to determine the flow and chemical behavior, whereas the liquid atomization was accounted for by LISA (Linear Instability Sheet Atomization) model incorporating also the cavitation within injection boundary condition. The boundary conditions were determined based on the data from the experimental hot water system. Depending on system requirements, especially with continuous physical processes as well as the results of experimental measurements, the paper reports on determination of the mixing field and its intensity in the turbulent flow, the description of heat release and interaction of turbulent flow field and chemical kinetics in the case of confined swirling flames.
Keywords: CFD, fluid dispersion, combustion, industrial burner, confined swirling flame, two-phase flow
Published in DKUM: 04.08.2017; Views: 1455; Downloads: 395
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33. Numerical simulation of force interactions between rigid bodies and fluid flowOžbej Verhnjak, 2017, master's thesis Abstract: Particles immersed in a fluid have always been an important researching domain in process technologies, pharmacy and fluid mechanics. It is for its practical utility in industry that the two-phase flow is still being academically researched, but in present times with a slightly different, more complex approach. Formerly all the particles have been assumed to be spheres, what simplified the models of processes physical presentation. Nowadays, however, it is clear that such an assumption makes significant errors in some fields of applications. With that reason ellipsoids were presented instead of spheres. That step also transferred computation from analytical or partially analytical to wholey numerical. This work presents the results of numerical simulation of different ellipsoids and sphere. In addition a Saffmann effect on sphere is presented as a special phenomena in fluid mechanics.
Keywords: OpenFOAM, Saffman effect, drag coefficient, sphere drag, drag on ellipsoids, forces on immersed bodies
Published in DKUM: 17.07.2017; Views: 1334; Downloads: 173
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34. Cooling analysis of a light emitting diode automotive fog lampMatej Zadravec, Matjaž Ramšak, Jure Ravnik, Matjaž Hriberšek, Jernej Slanovec, 2017, original scientific article Abstract: Efficiency of cooling fins inside of a light emitting diode fog lamp is studied using computational fluid dynamics. Diffusion in heat sink, natural convection and radiation are the main principles of the simulated heat transfer. The Navier-Stokes equations were solved by the computational fluid dynamics code, including Monte Carlo radiation model and no additional turbulence model was needed. The numerical simulation is tested using the existing lamp geometry and temperature measurements. The agreement is excellent inside of few degrees at all measured points. The main objective of the article is to determine the cooling effect of various heat sink parts. Based on performed simulations, some heat sink parts are found to be very ineffective. The geometry and heat sink modifications are proposed. While radiation influence is significant, compressible effects are found to be minor.
Keywords: heat transfer, cooling of electronic devices, cooling fins, light emitting diode automotive lamp, compressible flow
Published in DKUM: 07.07.2017; Views: 1564; Downloads: 407
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35. Uvod v računalniško dinamiko tekočinMatjaž Hriberšek, 2017, other educational material Abstract: Tradicionalne metode razvoja, ki temeljijo na tehniki preizkušanja in analitično-empiričnih računskih metodah, vse bolj nadomešča uporaba računalniških simulacijskih orodij. Da bi sodobni inženir lahko izkoristil potencial simulacijskih orodij, mora najprej dobro razumeti fizikalno dogajanje, na katerem temeljijo modeli v simulacijskih orodjih, prav tako pa mora imeti dobro znanje iz numeričnih metod, ki omogočijo računalniško rešitev v času in v prostorskih geometrijah. Zbrano gradivo iz področja računalniške dinamike tekočin (CFD) obravnava področje dinamike tekočin, ki je eno najzahtevnejših področij strojništva. Prvi del gradiva je namenjen razlagi numeričnih metod za pretvorbo parcialnih diferencialnih enačb dinamike toka v njihov algebrajski ekvivalent, ki je osnova računskih CFD algoritmov. Drugi del gradiva obravnava modeliranje robnih pogojev in turbulentnega toka, kar je najpomembnejši del uporabe CFD metod. Gradivo služi dopolnitvi predavanj iz predmeta Računalniška dinamika tekočin (CFD) na magistrskem študijskem programu Strojništvo, priporočam pa ga tudi študentom drugih tehniških študijskih programov.
Keywords: dinamika tekočin, numerične metode, računalniška dinamika tekočin, numerične simulacije
Published in DKUM: 06.02.2017; Views: 4152; Downloads: 365
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36. Določitev parametrov modela razprševanja in analiza tokovnih razmer v pretvorniku s selektivno katalitično redukcijoMatija Mlakar, 2016, master's thesis Abstract: Pred samim procesom simuliranja razmer v pretvorniku s selektivno katalitično redukcijo je bilo potrebno pridobiti podatke iz meritev, ki so bile narejene z PDA merilnim sistemom. Meritve v magistrski nalogi niso bile izvedene temveč so bili pridobljeni samo rezultati. Pridobljene meritve so bile nato uporabljene za določevanje parametrov razprševanja v programskem paketu AVL FIRE. Cilj določevanja parametrov je bil ta, da se zagotovi prileganje rezultatov simulacije na pridobljene meritve. Po uspešni določitvi parametrov sta bili narejeni dve CFD simulaciji. Prva je v geometriji vsebovala mešalo, ki skrbi za enakomerno porazdelitev NH3 pred vstopom v katalizator. V drugi simulaciji pa je bilo mešalo odstranjeno. Medsebojna primerjava rezultatov obeh simulacij je pokazala, da prinese mešalo v SCR sistem veliko več prednosti kot slabosti.
Keywords: CFD simulacija, določitev parametrov razprševanja, selektivna katalitična redukcija, analiza tokovnih razmer, mešalo
Published in DKUM: 07.10.2016; Views: 1503; Downloads: 163
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37. Primerjava učinkovitosti razprševanja plina s turbinskimi mešaliKarmen Potočnik, 2016, undergraduate thesis Abstract: Diplomsko delo obravnava razprševanje plina v kapljevini s turbinskim Rushtonovim mešalom, turbinskim mešalom s poševnimi lopaticami in poševnim disperzijskim diskom. Primerjali smo učinkovitost razprševanja, porabo moči in ostale parametre. Meritve so se izvajale na obstoječi laboratorijski napravi s pomočjo računalnika in programske opreme LabVIEW. Eksperiment je pokazal, da se učinkovitost dispergiranja plina za posamezna mešala razlikuje, prav tako potrebujejo mešala za mešanje različno moč. Najmanjšo moč za mešanje je potrebovalo turbinsko mešalo s poševnimi lopaticami, vendar ni uspelo učinkovito razpršiti plina. Kot najučinkovitejše se je izkazalo Rushtonovo mešalo, hkrati pa je to mešalo potrebovalo za mešanje največjo moč.
Keywords: mešanje, razprševanje plina, mešalo
Published in DKUM: 28.09.2016; Views: 1535; Downloads: 164
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38. Vpliv suhega zapolnjevanja sadre na koncentracijo delcev PM10 v zunanjem zrakuBernarda Podgoršek Kovač, 2016, master's thesis Abstract: Onesnaženost zraka z delci PM10 je vedno večji problem predvsem v mestih in ponekod tudi v njihovi okolici. Trdni delci so onesnaževala, ki zaradi povečanih koncentracij vplivajo na zdravje ljudi.
Na območju Celjske kotline so pomembni viri delcev različni industrijski obrati, kurišča, promet, resuspenzija in naravni viri. Na koncentracijo delcev PM10 vpliva tudi meteorologija, ki je v zimskem času neugodna (pogoste temperaturne inverzije).
Ker dosedanje raziskave še niso ocenile vpliva suhega zapolnjevanja sadre iz proizvodnje titanovega dioksida na lokaciji Za Travnik na koncentracijo delcev PM10 je bil namen naloge, da se to področje podrobneje razišče in rezultate primerja z rezultati modelnega izračuna pred uvedbo postopka suhega zapolnjevanja. Zato so se v okolici na več lokacijah izvedle meritve koncentracij delcev PM10. Zbrani vzorci so bili analizirani in določena je bila njihova sestava. Podatki so bil obdelani z statističnim modelom faktorske analize, ki temelji na analizi osnovnih komponent PCA (principal component analysis) za določevanje virov. Z ekstrakcijo faktorskega prostora smo pojasnili 68 % (77 %) meritev ter določili vire onesnaževanja, ki najbolj prispevajo k izmerjenim koncentracijam PM10 delcev [2]. Na lokacijah bliže opazovanega območja (vzhodni rob Celjske kotline) je bilo določeno, da je prevladujoči vir industrija jekla in nekovinska industrija, sledi ji promet, resuspenzija in mešani viri kurišča in industrija. Na lokaciji, ki je bila še bolj vzhodno pa so bila določena kot glavni vir kurišča na biomaso, sledijo kurišča na olje in kmetijstvo nato industrijski viri in resuspenzija, soljenje cest in/ali daljinski vpliv morja. Med slednje smo uvrstili tudi vir suhega zapolnjevanja sadre, ki ne vpliva signifikantno na koncentracije delcev PM10. Rezultati pridobljeni z modelnim izračunom so pokazali enake prevladujoče smeri širjenja delcev, napovedane koncentracije delcev iz vira suhega zapolnjevanja so bile bistveno večje od dejansko izmerjenih, zaradi precenjenega indeksa imisije in predpostavke, da do prašenja prihaja nepretrgoma in brez protiprašnih ukrepov, ki se izvajajo pri dejanskem suhem zapolnjevanju [23].
Keywords: Kakovost zunanjega zraka · Suho zapolnjevanje sadre · Delci PM10 · PCA analiza
Published in DKUM: 28.09.2016; Views: 1726; Downloads: 205
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39. Problematika komunalnega blata v čistilni napravi PtujAleksander Trep, 2016, undergraduate thesis Abstract: Predstavljen je problem komunalnega blata v čistilni napravi Ptuj. Blato je produkt čiščenja odpadne vode, ki nastaja na vseh čistilnih napravah. Glede na analize, ki so narejene na čistilni napravi Ptuj je ugotovljeno, da blato spada v drugi kakovostni razred ter ga je mogoče uporabiti pri sežigu ali so-sežigu. Prav tako bi bilo blato iz čistilne naprave Ptuj primerno za postopek pirolize.
Keywords: odpadna voda, blato
Published in DKUM: 27.09.2016; Views: 1672; Downloads: 232
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40. Določevanje moči za mešanje nenewtonske tekočine zmesi škroba in vodeKarolina Granfol, 2016, undergraduate thesis Abstract: V praksi se pogostokrat uporablja proces mešanja za najrazličnejše vrst tekočin, ki so lahko newtonske ali nenewtonske. Pri dimenzioniranju naprav za mešanje je pomembno določevanje potrebne moči za mešanje. Za nenewtonske tekočine, kot so dilatantne tekočine, je značilno, da je potrebna moč za mešanje odvisna od števila vrtljajev in tudi od viskoznosti, ki se pod vplivom strižnih napetosti spreminja. Predmet raziskave v tem delu je določevanje moči mešala za mešanje zmesi škroba in vode po postopku Rieger Novak. Meritve so pokazale, da je za različne gostote dilatantnih zmesi potrebna različna moč mešanja. Obravnavana zmes je izkazala lastnosti dilatantnih snovi.
Keywords: mešanje, dilatantna snov, Rushtonovo mešalo, določevanje moči za mešanje, eksperimentalna analiza
Published in DKUM: 26.09.2016; Views: 2483; Downloads: 352
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