1. Numerična analiza vpliva divergentnega kota na pojav kavitacije v venturijevem kanaluUrška Pitino, 2025, undergraduate thesis Abstract: V diplomski nalogi smo obravnavali vpliv divergentnega kota na pojav kavitacije v Venturijevem kanalu. Z uporabo numeričnih metod v programskem okolju ANSYS Fluent smo izvedli simulacijo nestacionarnega večfaznega toka z vodo in vodno paro. Uporabili smo Zwart-Gerber-Belamri kavitacijski model in primerjali rezultate za dva različna divergentna kota 4° in 12°. Analiza je pokazala, da večji divergentni kot povzroča intenzivnejše nastajanje kavitacijskih oblakov in njihovo pogostejše odcepljanje.
Keywords: kavitacija, Venturijev kanal, divergentni kot, numerična simulacija, računalniška dinamika tekočin, večfazni tok, ANSYS Fluent, kavitacijski oblak, Zwart-Gerber-Belamri.
Published in DKUM: 02.10.2025; Views: 0; Downloads: 15
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2. Analiza učinkovitosti športnega vesla glede na njegovo obliko z uporabo metode računalniške dinamike tekočinDomen Lešnik, 2025, undergraduate thesis Abstract: V diplomskem delu je bila izvedena primerjava učinkovitosti športnih vesel s pomočjo simulacij računalniške dinamike tekočin. Kot glavni pokazatelj učinkovitosti vesla je bila upoštevana sila, ki deluje na veslo pri določeni hitrosti zaveslaja v smeri plovbe. Za lažjo primerjavo je bila pri vseh analiziranih vrstah vesel uporabljena enaka hitrost zaveslaja. Simulacije so bile opravljene v računskem volumnu ob uporabi robnih pogojev, s katerimi so bili simulirani realni pogoji pri športnem veslanju. Poleg rezultatov simulacij diplomsko delo vključuje tudi opis modeliranja, analizo kakovosti računskega območja in predstavitev uporabljenih robnih pogojev.
Rezultati simulacije kažejo, da so najučinkovitejše oblike vesel vesla tipa »sekira«, kar je skladno z njihovo pogosto uporabo v praksi. Kot najuspešnejša se je izkazala oblika Sekira 2v3, vendar so razlike v učinkovitosti med vsemi tremi izvedbami lopatice tipa »sekira« zelo majhne in praktično zanemarljive. To pomeni, da vse analizirane izvedbe tega tipa dosegajo podobno visoko raven potisne učinkovitosti.
Keywords: računalniška dinamika tekočin (RDT), numerična analiza, rotirajoča domena, športno veslanje, učinkovitost vesla
Published in DKUM: 25.09.2025; Views: 0; Downloads: 12
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4. Vetrne turbineIgnacijo Biluš, Luka Kevorkijan, Luka Lešnik, 2025 Abstract: Publikacija obravnava vetrne turbine. V prvem, uvodnem poglavju so podane temeljne značilnosti oskrbe z energijo v Sloveniji in potencial za izkoriščanje obnovljivih virov s poudarkom na energiji vetra. Temu sledi poglavje o vetru v katerem je pojasnjen nastanek vetrov, značilnosti vetrov s porazdelitvijo hitrosti, vplivom reliefa in turbulence na energijo vetra. V poglavju je predstavljena metodologija za ocenjevanje razpoložljivosti vetrov in možnosti pridobivanja energije. V tretjem poglavju je podana matematična formulacija dinamike toka v konvencionalnih vetrnih turbinah s horizontalno osjo. Predstavljene so metode s katerimi je možno ovrednotiti učinkovitost energijske izmenjave in temeljni postopki za oblikovanje lopatic vetrnih turbin. V četrtem poglavju je predstavljen okoljski vidik umestitve vetrnih turbin v naravo. Obravnavan je vpliv vetrnih turbin na živali, degradacija pokrajine zaradi vizualnega vpliva in hrup, ki ga povzročajo vetrne turbine.
Keywords: obnovljivi viri energije, veter, vetrna turbina, dinamika toka, vpliv na okolje
Published in DKUM: 16.07.2025; Views: 0; Downloads: 41
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5. Cavitation erosion modelling on a radial divergent test section using RANSLuka Kevorkijan, Luka Lešnik, Ignacijo Biluš, 2022, original scientific article Abstract: Cavitation is the phenomenon of fluid evaporation in hydraulic systems, which occurs due to a pressure drop below the value of the vapor pressure. For numerical modelling of this generally undesirable phenomenon, which is often associated with material damage (erosion), there are various mathematical vapor transfer models that have been validated in the past. There are different approaches to predicting cavitation erosion, which have mostly been experimental in the past. Recently various numerical models have been developed with the development of numerical simulations. They describe the phenomenon of cavitation erosion based on different theoretical considerations, such as Pressure wave hypothesis, Microjet hypothesis, or a combination of both. In the present paper, an analysis of the Schnerr-Sauer transport cavitation model was used, upgraded with an erosive potential energy model based on pressure wave hypothesis for cavitation erosion prediction. The extended numerical model has been applied to the case of a radial divergent test section in three different mathematical formulations. The results of simulation were compared and validated to experimental work performed by other authors. The study shows that the distribution of surface accumulated energy agrees with the experimental results, although certain differences exist between formulations. The applied method appears to be appropriate for further use, and to be extended to materials response modelling in the future.
Keywords: kavitacija, erozija, erozivna potencialna energija, numerične simulacije, cavitation, erosion, erosive potential energy, numerical simulation
Published in DKUM: 26.03.2025; Views: 0; Downloads: 7
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6. Settling of mesoplastics in an open-channel flowLuka Kevorkijan, Elvis Žic, Luka Lešnik, Ignacijo Biluš, 2022, original scientific article Abstract: Pollution of water by plastic contaminants has received increasing attention, owing to
its negative effects on ecosystems. Small plastic particles propagate in water and can travel long
distances from the source of pollution. In order to research the settling motion of particles in
water flow, a small-scale experiment was conducted, whereby spherical plastic particles of varying
diameters were released in an open-channel flow. Three approaches were investigated to numerically
simulate the motion of particles. The numerical simulation results were compared and validated
with experimental data. The presented methods allow for deeper insight into particle motion in
fluid flow and could be extended to a larger scale to predict the propagation of mesoplastics in
natural environments.
Keywords: dense discrete phase model, discrete element method, diameter, discrete phase model, mesoplastics, particles, settling
Published in DKUM: 20.03.2025; Views: 0; Downloads: 9
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7. Numerična simulacija vbrizgavanja piroliznega olja iz odpadne LDPE plastike v vbrizgalni šobi dizelskega motorja : diplomsko delo univerzitetnega študijskega programa I. stopnjeAndraž Dobaj, 2024, undergraduate thesis Abstract: Proučevan je bil vpliv dodatka piroliznega olja, pridobljenega iz polietilena nizke gostote dizelskemu gorivu na pojavnost kavitacije v vbrizgalni šobi dizelskega motorja. V numerični simulaciji s programsko opremo Ansys Fluent so bile upoštevane lastnosti treh različnih goriv: čistega dizelskega goriva, dizelskega goriva z dodatkom 10% in 20% piroliznega olja (volumski deleži). Analiza rezultatov je pokazala, da dodajanje piroliznega olja dizelskemu gorivu vpliva na pojavnost kavitacije. Najnižja pojavnost kavitacije je bila zabeležena pri sto odstotnem dizelskem gorivu, najvišja pa pri gorivu z dodatkom 20% piroliznega olja. Pirolizno olje, pridobljeno iz polietilena nizke gostote ima nižji vrednosti viskoznosti in gostote kot dizelsko gorivo. Možno je sklepati, da nižji vrednosti viskoznosti in gostote vplivata na večjo pojavnost kavitacije pri gorivu z višjim volumskim deležem piroliznega olja iz polietilena nizke gostote v zmesi.
Keywords: kavitacija, računalniška dinamika tekočin, pirolizno olje, polietilen nizke gostote, vbrizgalna šoba, dizelski motor
Published in DKUM: 08.01.2025; Views: 0; Downloads: 40
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8. Sklopljen računski model za napoved erozije hidravličnih sistemov zaradi kavitacije in delcev : doktorska disertacijaLuka Kevorkijan, 2024, doctoral dissertation Abstract: Hidravlični sistemi so lahko podvrženi eroziji zaradi pojava kavitacije ali zaradi prisotnosti delcev v toku tekočine. V hidravličnih sistemih je pogosto prisotna hidrodinamska kavitacija, ki je posledica spremenjene dinamike toka, kjer pride do lokalnega povečanja hitrosti in posledičnega padca tlaka do tlaka uparjanja. Na trdni površini, ki je izpostavljena toku s kavitacijo, se lahko pojavi erozija zaradi kavitacije. Ob tem so lahko v tekočini tudi suspendirani delci, ki se ob trku s trdno površino odbijejo in pri tem oddajo del gibalne količine steni zaradi česar lahko nastopi erozija trdne površine. Ob poznavanju mehanizmov in sposobnosti modeliranja erozije zaradi kavitacije in delcev ostaja odprto področje hkratna obravnava pri modeliranju erozije zaradi obeh pojavov. Zato je bil razvit numeričen model za napoved erozije hidravličnih sistemov zaradi kavitacije in delcev. Numerični model sestoji iz modela homogene zmesi za večfazni tok, kjer je kavitacija modelirana z izvornim členom v dodatni prenosni enačbo mase pare, ki ga podaja Schnerr-Sauer kavitacijski model. Gibanje delcev je modelirano po pristopu Lagrangevega sledenja z dvosmernim sklapljanjem gibalne količine med delcem in tekočino. V komercialni program za računalniško dinamiko tekočin je preko uporabniško definiranih funkcij vpeljan model kavitacijske erozije. Erozija delcev je modelirana z McLaury modelom. Turbulenca je modelirana s tremi različnimi modeli, dvema RANS (k-ε RNG in k-ω SST) in enim hibridnim (DDES-SST). Z namenom validacije so izvedeni tudi eksperimenti s kavitacijo v toku z delci in brez delcev pri treh pretokih na primeru Venturijevega kanala, kjer erozijo na površini posredno napovemo z metodo barvnega nanosa. Narejena je primerjava rezultatov numeričnih simulacij z različnimi turbulentimi modeli, kjer je ugotovljeno, da daje najboljšo napoved DDES-SST model. Pri treh pretokih toka brez delcev in z delci je ugotovljeno zadovoljivo ujemanje med simulacijo in eksperimentom, s čimer je potrjena ustreznost numeričnega modela za napoved erozije zaradi kavitacije in zaradi delcev.
Keywords: kavitacija, delci, erozija
Published in DKUM: 22.10.2024; Views: 0; Downloads: 52
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9. The ǂeffect of fuel quality on cavitation phenomena in common-rail diesel injector—a numerical studyLuka Kevorkijan, Ignacijo Biluš, Eloisa Torres Jiménez, Luka Lešnik, 2024, original scientific article Abstract: Plastic is one of the most widely used materials worldwide. The problem with plastic
arises when it becomes waste, which needs to be treated. One option is to transform plastic waste
into synthetic fuels, which can be used as replacements or additives for conventional fossil fuels
and can contribute to more sustainable plastic waste treatment compared with landfilling and other
traditional waste management processes. Thermal and catalytic pyrolysis are common processes
in which synthetic fuels can be produced from plastic waste. The properties of pyrolytic oil are
similar to those of fossil fuels, but different additives and plastic stabilizers can affect the quality
of these synthetic fuels. The quality of fuels and the permissible particle sizes and number density
are regulated by fuel standards. Particle size in fuels is also regulated by fuel filters in vehicles,
which are usually designed to capture particles larger than 4 µm. Problems can arise with the
number density (quantity) of particles in synthetic fuels compared to that in fossil fuels. The present
work is a numerical study of how particle size and number density (quantity) influence cavitation
phenomena and cavitation erosion (abrasion) in common-rail diesel injectors. The results provide
more information on whether pyrolysis oil (synthetic fuel) from plastic waste can be used as a
substitute for fossil fuels and whether their use can contribute to more sustainable plastic waste
treatments. The results indicate that the particle size and number density slightly influence cavitation
phenomena in diesel injectors and significantly influence abrasion.
Keywords: plastic waste, synthetic fuels, pyrolytic oil, common rail, cavitation, erosion, particles
Published in DKUM: 05.07.2024; Views: 131; Downloads: 20
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10. Obtaining the synthetic fuels from waste plastic and their effect on cavitation formation in a common-rail diesel injectorLuka Kevorkijan, Amalia Palomar-Torres, Eloisa Torres Jiménez, Carmen Mata, Ignacijo Biluš, Luka Lešnik, 2023, original scientific article Abstract: The presented paper addresses two significant issues of the present time. In general, the studies of the effect of synthetic fuels on cavitation formation and cavitation erosion prediction in the nozzle tip of common-rail diesel injectors were addressed. The first problem is plastic waste, which can have a significant negative environmental impact if not treated properly. Most plastic waste has high energy value, so it represents valuable material that can be used in resource recovery to produce various materials. One possible product is synthetic fuel, which can be produced using thermal and catalytic pyrolysis processes. The first issue addressed in the presented paper is the determination of fuel properties since they highly influence the fuel injection process, spray development, combustion, etc. The second is the prediction of cavitation development and cavitation erosion in a common-rail diesel injector when using pyrolytic oils from waste plastic. At first, pyrolytic oils from waste high- and low-density polyethylene were obtained using thermal and catalytic pyrolysis processes. Then, the obtained oils were further characterised. Finally, the properties of the obtained oils were implemented in the ANSYS FLUENT computational program and used in the study of the cavitation phenomena inside an injection nozzle hole. The cavitating flow in FLUENT was calculated using the Mixture Model and Zwart-Gerber-Belamri cavitation model. For the modelling of turbulence, a realisable k–ε model with Enhanced Wall Treatment was used, and an erosion risk indicator was chosen to compare predicted locations of cavitation erosion. The results indicate that the properties of the obtained pyrolytic oils have slightly lower density, surface tension and kinematic viscosity compared to conventional diesel fuel, but these minor differences influence the cavitation phenomenon inside the injection hole. The occurrence of cavitation is advanced when pyrolytic oils are used, and the length of cavitation structures is greater. This further influences the shift of the area of cavitation erosion prediction closer to the nozzle exit and increases its magnitude up to 26% compared to diesel fuel. All these differences have the potential to further influence the spray break-up process, combustion process and emission formation inside the combustion chamber.
Keywords: plastic waste, synthetic fuels, pyrolytic oils, common-rail, cavitation, erosion, transient simulation
Published in DKUM: 18.03.2024; Views: 299; Downloads: 41
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