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V magistrskem delu so predstavljeni rezultati simulacije konvektivnega vrenja v navpičnem kanalu, ki smo jih izvedli s programom za računalniško dinamiko tekočin ANSYS Fluent. Uporabili smo Eulerjev dvofluidni pristop, ki temelji na fazno povprečenih fizikalnih količinah. Modelirali smo turbulenco, medfazni prenos gibalne količine, energije in mase. Za modeliranje vrenja na steni smo uporabili model razdelitve toplotnega toka. Velikost mehurčka smo modelirali s populacijskim modelom, ki upošteva rast mehurčkov zaradi uparjanja, krčenje zaradi kondenzacije, združevanje zaradi trkov in razpade zaradi turbulence. Rezultate smo primerjali s tremi različnimi eksperimentalnimi primeri DEBORA eksperimentov pri različnih pogojih. Primerjali smo porazdelitve glavnih parametrov dvofaznega toka, kot so volumski delež pare, povprečna velikost mehurčkov in temperatura kapljevine. Na enem primeru smo podrobneje raziskali delovanje populacijskega modela. Analizirali smo vpliv števila velikostnih razredov mehurčkov, temperature kapljevine in stene ter modela razdelitve toplotnega toka. In this master thesis the results of convective boiling simulations using the ANSYS Fluent code are presented. The two-phase flow is described using the Eulerian two-fluid model framework, that is based on the phase averaged equations. Simulations are done with consideration of turbulent momentum, heat and mass transfer between the phases. For wall boiling the heat partitioning model is used. Bubble sizes are modelled using the population balance model that accounts for bubble growth and shrinkage due to evaporation and condensation, coalescence due to collisions and breakage due to turbulence. Simulation results are compared with the experimental results of three different DEBORA cases at different operating conditions. Distributions of main two-phase flow parameters such as void fraction, the average bubble size and the liquid temperature are compared. On one of the cases, the population balance model is studied in more detail. The influence of bubble classes, the liquid temperature, the wall temperate and the effect of heat flux partitioning model is analysed.

Razvili smo dušilec za komprimiran zrak. Uporaben je na adsorpcijskih sušilnikih zraka, ki pri delovanju povzročijo izpust večje količine komprimiranega zraka iz rezervoarja, pri tem pa nastane hrup. V nalogi smo izdelali več idejnih rešitev, katere smo preverili z računalniško simulacijo tekočin, nekatere smo pa tudi eksperimentalno preverili in primerjali z obstoječo rešitvijo. Najboljša eksperimentalna rešitev nakazuje znižanje hrupnosti za približno 6 dB, kar ustreza približno 4x nižja zvočna raven hrupa. We developed a compressed air silencer. It is useful on adsorption air dryers, which cause a large amount o fair to be released during operation, creating noise. In the thesis, we created several conceptual solutions, which we tested with computational fluid dynamics, some of the solutions were also tested experimentally and compared to the existing solution. The best experimental solution suggests a noise reduction of about 6 dB, which corresponds to about 4x lower sound levels of noise.

Izgradnja rečnih pregrad pomeni prekinitev nujno potrebnih migracijskih poti za ribe in druge vodne organizme za ohranitev populacij vzdolž vodotokov. Eden izmed omilitvenih ukrepov ob takšnih posegih v rečno telo je izgradnja ribje steze, po kateri vodni organizmi predvsem ob času drsti migrirajo ob sami pregradi. V članku so podrobno prikazani numerični parametri matematičnega modela PCFLOW2D, ki se je ob ustreznih nastavitvah izkazal kot ustrezno orodje za projektiranje ribjih stez z vertikalnimi režami. Prikazana je analiza vpliva geometrijskih in numeričnih parametrov na izračun tokovne slike. Podrobno so prikazane meritve toka v že zgrajeni ribji stezi ob hidroelektrarni Arto-Blanca, na podlagi katerih je bil matematični model validiran. Prikazani so rezultati izračunov za različne vzdolžne padce ribje steze. Poleg največjih hitrosti in pretoka so bili analizirani še drugi pomembni hidravlični parametri, ki vplivajo na prehodnost ribje steze, kot sta hitrostno polje in porazdelitev disipacije turbulentne kinetične energije znotraj posameznega prekata ribje steze. River dams interrupt essential migration routes of fish and other aquatic organisms. One of the most important mitigation measures that enable aquatic fauna to migrate, especially during spawning, are fishways. The paper presents all the main results of the numerical model PCFLOW2D, which proved to be a useful tool in designing a vertical slot fishway (VSF). The presented analysis includes the quantification of the effect of various numerical and geometrical parameters. Extensive field measurements of flow characteristics in the operating fishway at the hydro power plant Arto-Blanca, which are employed for the model's validation, are discussed as well. The results of simulations for various longitudinal slopes of the VSF are presented. In addition to maximum flow velocities and discharge, other important hydraulic parameters affecting fishway efficiency were analyzed, such as velocity field and distribution of turbulent kinetic energy dissipation.

Pri razvoju malih črpalk za pomoč levemu ventriklu pešajočega srca se v zadnjih dvajsetih letih vedno bolj uporablja računalniška dinamika tekočin, ki je ob primerni validaciji zelo uporabno orodje pri snovanju naprav. Pri doktorski disertaciji smo se osredotočili na simulacije enofaznega toka Newtonske tekočine pri konstantni temperaturi ob uporabi naprednih turbulentnih modelov družin DES in SAS, jih primerjali s široko uporabljenim SST-k? modelom in jih na koncu validirali z eksperimentom. Naloga je sestavljena iz treh delov (raziskav). Pri I. raziskavi smo izvedli preliminarni splošni preizkus na enostavni geometriji iztočne šobe, ki je bila del iniciative za razvoj numeričnih simulacij s strani Uprave ZDA za hrano in zdravila (ang. Federal Drug Administration- FDA). Pri II. raziskavi smo primerjali tokovne karakteristike ?p(Q) male komercialne črpalke HeartAssist5 z vodo in jih validirali. Pri III. raziskavi pa je bila napravljena raziskava na transparentnem preizkuševališču, izdelanem po geometriji komercialne črpalke aVAD, kjer smo numerične simulacije primerjali z merilno metodo PIV. Ugotovili smo, da se pri nominalnih delovnih pogojih naprav najbolje ujemata z eksperimentalnimi podatki napredna turbulentna modela SBES (I. in III. raziskava) in SAS (II. raziskava). SBES turbulentni model je zadnja nadgradnja modela-DES. Kriteriji, po katerih so modeli primerjani, so primerljivi računski časi izračunov na enakih numeričnih mrežah, enakem številu računskih jeder superračunalnika ter ujemanju eksperimentalnih parametrov izračunanih hitrosti in tlaka v primerjavi z numerični simulacijami. During the development process of the left ventricular assist devices (LVAD) the computational fluid dynamics (CFD) is increasingly used which is a valuable tool if validated with the experiment. In this thesis we have focused on CFD simulations of one phase, newtonian flow with a constant temperature using advanced turbulence models from DES family and SAS formulation. The comparison has been performed with widely used SST-kω model and all cases have been validated experimentally. Our task was divided into three parts (research cases). In the first case we have investigated the nozzle benchmark which was a part of a Food and Drug Administration (FDA) backed research iniciative with the goal to promote the CFD in mechanics in medicine. In the second case the Δp(Q) flow characteristics were compared in small commercial HeartAssist 5 LVAD using water as fluid. In the third case the investigation was performed on a transparent housing built on a comercial aVAD small pump, where the numerical simulations were compared with the results of Particle Image Velociometry (PIV) method. It has been concluded that the best results were obtained by SBES (I. and III. research case) and SAS turbulence models (II. research case). SBES turbulence model is the latest most updated derivative of the DES model. The criteria for the comparison was chosen like velocity, pressure difference and simulation time on the same hardware setup.

Dolgi potovalni časi so vse bolj pogosti, s tem pa postaja toplotno ugodje v kabini osebnega vozila eden najpomembnejših vidikov ugodja med vožnjo pri vseh spremenljivih vremenskih pogojih. S pomočjo vročežičnih anemometrov je bila izmerjena lokalna hitrost in temperatura zraka v vozilu Nissan Micra, ter določena kategorija toplotnega okolja. V njem je bila z metodo infrardeče termografije opravljena vizualizacija toka zraka iz zračnikov. Med eksperimentom je bilo težko doseči konstanto temperaturo zraka zaradi ročne klima naprave, ki temperature ne nadzoruje in tako svojega delovanja ne more avtomatsko prilagajati. Thermal comfort is one of the most important factors regarding feelings of comfort experienced by humans in a vehicle cabin. Even more so with increasing time spent on roads and different thermal loads it is exposed to. In the experimental part of the Final thesis we measured local air temperatures and velocities in Nissan Micra interior, with the use of two hot wire anemometers. Indoor environment category was also determined for the aforementioned cabin. Method of infrared thermography was used for visualization of non-isothermal air flow out of a rectangular vent. During the experiment the air temperature had to be held constant, which was hard to achieve with a manual air conditioning system.

V zaključni nalogi smo obravnavali ugodje človeka v prostoru in poudarili vpliv turbulence zraka v zaprtih prostorih na občutek prepiha. Opisali smo vse ključne dejavnike, ki so del človekovega ugodja v notranjem prostoru. Obravnavali smo tudi PMV in PPD model ter model prepiha. Z eksperimentom, primerljivim z eksperimenti znanstvenikov z istega področja, v katerem je sodelovalo 20 prostovoljcev, smo dokazali, da gibanje zraka opazno vpliva na človekovo toplotno ugodje. Nato smo rezultate grafično prikazali in ustrezno obravnavali. In the final thesis we discused the comfort of a person being indoors and emphasized the effect of air turbulence on the perception of draught in a closed room. We described all the key factors that are a part of humans comfort in indoor environment. We also discussed PMV, PPD and draught models. An experiment, comparable to various experiments of scientists from the same field, involving 20 volunteers, demonstrated that the movement of the air noticebly affects human's thermal comfort. Then we graphically displayed the results and discussed it appropriately.

V okviru magistrskega dela je bila opravljena validacija numerične simulacije dinamičnega pojava tokovno povzročenega zvoka. Podana je bila ustrezna teoretična podlaga, sledi integralna obravnava elementa z značilnim pojavom žvižga v obliki eksperimenta, ki se je izvedel v Laboratoriju za energetske delovne stroje in tehnično akustiko na Fakulteti za strojništvo v Ljubljani. Osrednji del magistrskega dela zajema nastavitve in zagon numerične simulacije v programskem okolju Fluent. Sledi analiza vplivnih spremenljivk s pomočjo hitre Fourierjeve transformacije in slikovna obdelava animacije tokovnega polja z lastno programsko kodo. Slednje je izkazalo soodvisnost značilnih amplitud v frekvenčni domeni tokovnega polja in akustičnega pojava. Within presented thesis validation of numerical simulation regarding dynamic phenomenon of flow generated sound was performed. An appropriate theoretical basis was given, followed by the integral processing of an element with a typical phenomenon of whistle in the form of an experiment carried out in the Laboratory for pumps, compressors and technical acoustics at the Faculty of mechanical engineering in Ljubljana. The main part of the master's thesis covers the settings and start of numerical simulation in the Fluent programming environment. The analysis of influential variables is followed by the fast Fourier transformation of the sound field and the image processing of the animation of the flow field with our own program code is done. The latter showed the interdependence of the characteristic amplitudes in the frequency domain of the flow field and the acoustic phenomenon.

V nalogi je narejena primerjava med eksperimentalnim in numeričnim modeliranjem uparjanja vode v vertikalnem kanalu. Poudarek je na obravnavi dvofaznega toka tekočine z uporabo programskega paketa ANSYS CFX. Ugotovili smo, da lahko s pomočjo tega programa precej natančno opišemo tako uparjanje vode kot tudi tok brez uparjanja. This diploma thesis represents comparison between experimental and numerical modelling of water boiling in a vertical pipe. Emphasis is on modelling two phase flows using ANSYS CFX software package. We found that ANSYS CFX is very suitable for calculations of characteristics of either water boiling or water flow without boiling.