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1.
Cavitation erosion modelling on a radial divergent test section using RANS
Luka 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: 3
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2.
Settling of mesoplastics in an open-channel flow
Luka 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: 4
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3.
Hidroenergetski sistemi
Ignacijo Biluš, 2024

Abstract: Skripta obravnava hidroenergetske sisteme. V uvodu so podane temeljne značilnosti oskrbe z energijo v Sloveniji, nato so predstavljeni obnovljivi viri energije in hidroenergija. Temu sledita poglavji o hidrologiji in hidroelektrarnah. V slednjem je podana osnovna razdelitev hidroelektrarn in predstavljen način njihovega delovanja. Na integralni ravni so obravnavani tudi energijski parametri vodnih turbin. Ločena poglavja so namenjena obravnavi konvencionalnih vodnih turbin in njihovih obratovalnih karakteristik. Zadnje poglavje obravnava pojav kavitacije v vodnih turbinah. Definirane so pojavne oblike glede na vrsto vodne turbine in vpliv tega pojava na integralne obratovalne karakteristike.
Keywords: obnovljivi viri energije, hidroelektrarne, vodna turbina, obratovalne karakteristike, kavitacija
Published in DKUM: 22.11.2024; Views: 0; Downloads: 27
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4.
Sklopljen računski model za napoved erozije hidravličnih sistemov zaradi kavitacije in delcev : doktorska disertacija
Luka 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: 39
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5.
Merjenje pretoka vode v cevi z ultrazvočnim merilnikom
Timotej Jezernik, 2024, undergraduate thesis

Abstract: V diplomskem delu je opisano merjenje pretoka vode s pomočjo ultrazvočnega merilnika pretoka. Primerjali smo dva ultrazvočna merilnika, FUJI PORTAFLOW X in TDS - 100H. Merjenje pretoka se je izvajalo na šolski progi za preizkušanje črpalk. Za referenčno metodo je bilo uporabljeno merjenje pretoka z zaslonko. V prvem delu diplomskega dela je predstavljeno merjenje pretoka na splošno in delovanje ultrazvočnih merilnikov. Sledijo opis priprave na merjenje, protokol merjenja in izvajanje meritev. Po končanem merjenju je prikazana analiza in obdelava podatkov, pridobljenih s pomočjo izvajanja meritev. Opisani so tudi vplivi pozicij merjenja in primerjava med posameznimi metodami. Podani so še zaključki in napotki za nadaljnjo raziskavo na omenjenem področju.
Keywords: merjenje pretoka vode, ultrazvok, primerjava meritev, doseganje točnosti, napotki za merjenje
Published in DKUM: 30.09.2024; Views: 0; Downloads: 42
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6.
The ǂeffect of fuel quality on cavitation phenomena in common-rail diesel injector—a numerical study
Luka 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: 16
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7.
Optimizacija geometrije ladijskega vijaka na tokovno brazdo ladijskega trupa : magistrsko delo
Jure Vobner, 2024, master's thesis

Abstract: Različni ladijski trupi ustvarjajo različne tokovne brazde. S pomočjo računalniške dinamike tekočin je optimirana interakcija ladijskega vijaka in trupa. Za zmanjšanje računskega časa je geometrija lopatice razdeljena na dvodimenzionalne medsebojno sklopljene domene. Robni pogoji znotraj teh domen so pogojeni z osnovno numerično simulacijo interakcije vijaka in trupa. V dvodimenzionalnem prostoru je izvedena optimizacija oblike hidrodinamičnih profilov. Avtonomni vnos geometrijskih modifikacij je zagotovljen s parametričnim modeliranjem. Uspešnost optimizacije je ovrednotena preko integralnih veličin in pripadajočih obratovalnih karakteristik. Uporaba optimizacijskih algoritmov in upoštevanje dejanskih tokovnih razmer pred ladijskim vijakom znatno doprinese k izboljšanju njegove učinkovitosti. Boljši izkoristek ladijskega vijaka pripomore k trajnostnemu razvoju pomorske industrije, saj zniža porabo goriva in pripadajoče emisije toplogrednih plinov.
Keywords: ladijski vijak, računalniška dinamika tekočin, večfazni tok, optimizacijski algoritem, obratovalne karakteristike
Published in DKUM: 28.03.2024; Views: 218; Downloads: 40
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8.
Obtaining the synthetic fuels from waste plastic and their effect on cavitation formation in a common-rail diesel injector
Luka 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: 36
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9.
Experimental analysis of cavitation erosion in a particle-laden flow
Filip Jovanovski, 2023, undergraduate thesis

Abstract: Cavitation erosion is a problem that presents a challenge for the engineers in different industries, as it erodes the machinery which leads to lower efficiency and higher maintanance costs. An experimental investigation has been conducted to evaluate cavitation and cavitation erosion with and without the presence of solid particles in a Venturi channel. The methodology is based on observing and analysing the evolution of the vapour structures and occurence of cavitation erosion on the sample surface in the Venturi channel. To conduct experiments the cavitation tunnel was used, with the central component being a transparent test section with a Venturi-like channel (constructed from Plexiglass walls and a metal insert) to monitor the process of cavitation. To detect the damage caused by cavitation erosion and abrasion, the most effective solution was found to be an indicator in the form of black acrylic paint thinned with water (at a ratio of 1:2). On the sample surface, a self-adhesive aluminium tape was applied to protect the aluminium base from erosive characteristics from cavitation Furthermore, a comparison between cavitation with and without solid particles was made to determine the effects of solid particles on both cavitation and abrasion of the sample surface. The observation revealed that no matter the solid particles, damage from cavitation erosion appears at the separation point and in proximity to the location of the detached cloud collapse. The spherical glass particles with diameters between 40 µm and 70 µm added an abrasive effect on the sample surface only in the presence of cavitation structures. It was determined, that the intensity of cavitation erosion and abrasion increases when the cavitation number decreases and volumetric flow rate increases. Also, an economic analysis was conducted, to determine which is the more cost beneficial solution between replacement of the metal insert and application of protective coatings over the metal insert.
Keywords: cavitation erosion, solid particles, abrasion, experiment
Published in DKUM: 28.02.2024; Views: 230; Downloads: 32
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10.
Cavitation erosion modelling : comparison of different driving pressure approaches
Luka Kevorkijan, Marko Pezdevšek, Ignacijo Biluš, Gorazd Hren, 2023, original scientific article

Abstract: In this paper we compared different driving pressure approaches to calculate the cavitation potential energy from a source, which is transferred to a surface. The first approach used the reference pressure, the second approach used the pressure calculated at each timestep with no averaging, the third approach used the averaged pressure values from all timesteps included in one shedding cycle, and the last approach used pressure values from the steady state simulations results. The results show that for all formulations the averaged pressure values and steady state pressure values give similar results in terms of mean potential power distribution on the hydrofoil surface as in absolute values. The reference pressure approach gave similar results for the derivative and divergence formulation while for the source term the mean potential power distribution on the hydrofoil surface differs and the maximums were near the leading edge. The approach where we used no pressure averaging gave adequate results in terms of mean potential power distribution but differs from other approaches in absolute values which were considerably lower for all potential power formulations.
Keywords: cavitation, erosion potentional, driving pressure, numerical simulations
Published in DKUM: 21.02.2024; Views: 400; Downloads: 279
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