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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, izvirni znanstveni članek

Opis: 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.
Ključne besede: plastic waste, synthetic fuels, pyrolytic oils, common-rail, cavitation, erosion, transient simulation
Objavljeno v DKUM: 18.03.2024; Ogledov: 87; Prenosov: 5
.pdf Celotno besedilo (4,55 MB)
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Experimental analysis of cavitation erosion in a particle-laden flow
Filip Jovanovski, 2023, diplomsko delo

Opis: 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.
Ključne besede: cavitation erosion, solid particles, abrasion, experiment
Objavljeno v DKUM: 28.02.2024; Ogledov: 85; Prenosov: 13
.pdf Celotno besedilo (3,93 MB)

Cavitation erosion modelling : comparison of different driving pressure approaches
Luka Kevorkijan, Marko Pezdevšek, Ignacijo Biluš, Gorazd Hren, 2023, izvirni znanstveni članek

Opis: 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.
Ključne besede: cavitation, erosion potentional, driving pressure, numerical simulations
Objavljeno v DKUM: 21.02.2024; Ogledov: 159; Prenosov: 3
.pdf Celotno besedilo (796,29 KB)
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Reversible pump-turbines - a study of pumping mode off-design conditions
Uroš Ješe, Aleš Skoták, 2020, izvirni znanstveni članek

Opis: The role of pumped storage power plants (PSP) in electrical grid systems has been changing in recent years. Demands for switching from pumping to generating mode are becoming increasingly frequent. Moreover, the operating ranges of the reversible pump-turbines used in PSP systems are becoming wider in order to use the PSP as a regulator and a stabilizer of the electrical grid. The primary challenges in the development of pump-turbines are the hydraulic instabilities that occur in pumping and generating modes. The present paper focuses on partial load pumping mode instabilities, such as cavitation and rotating stall. Modern tools, such as CFD, are used for the analysis of the phenomena along with conventional experimental approaches. Rotating stall has been investigated in hydraulic laboratory experimentally and reproduced numerically using commercial CFD code. Three rotating stall cells with a rotational frequency of 2.5% of nominal pump-turbine frequency have been identified. Cavitating vortices related to rotating stall were found in the guide vanes region. Both phenomena indicate highly unstable and potentially dangerous operating conditions that need to be investigated in detail. Understanding the causes for the instabilities will lead to an improved pump-turbine design that will enable safer, more flexible and more reliable operating with fewer unwanted instabilities.
Ključne besede: pump-turbine, rotating stall, cavitation, Pumping mode instabilities
Objavljeno v DKUM: 01.12.2023; Ogledov: 230; Prenosov: 3
.pdf Celotno besedilo (2,46 MB)
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Comparison of cavitation models for the prediction of cavitation around a hydrofoil
Marko Pezdevšek, Ignacijo Biluš, Gorazd Hren, 2021, izvirni znanstveni članek

Opis: In this paper, four different cavitation models were compared for predicting cavitation around a hydrofoil. A blocked structured mesh was created in ICEM CFD. Steady-state 2D simulations were performed in Ansys CFX. For all cases, the SST turbulence model with Reboud's correction was used. For Zwart and Schnerr cavitation models, the recommended values were used for the empirical coefficients. For the full cavitation model and Kunz cavitation model, values for the empirical coefficients were determined as the recommended values did not provide satisfactory results. For the full cavitation model, the effect of non-condensable gases was neglected. For all the above-mentioned cavitation models, the pressure coefficient distribution was compared to experimental results from the literature.
Ključne besede: hydrofoil, cavitation, Ansys CFX
Objavljeno v DKUM: 10.11.2023; Ogledov: 274; Prenosov: 6
.pdf Celotno besedilo (1,90 MB)
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Numerical prediction of cavitation erosion on a hydrofoil
Marko Pezdevšek, Andrej Predin, Matej Fike, Gorazd Hren, 2022, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: hydrofoil, cavitation, erosion, Ansys CFX
Objavljeno v DKUM: 30.10.2023; Ogledov: 210; Prenosov: 4
.pdf Celotno besedilo (14,78 MB)
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Prediction of cavitation and particle erosion in a radial divergent test section
Luka Kevorkijan, Luka Lešnik, Ignacijo Biluš, 2022, izvirni znanstveni članek

Opis: The 3D unsteady, cavitating, particle-laden flow through a radial divergent test section was simulated with the homogeneous mixture model and Discrete Phase Model (DPM) within the commercial CFD code ANSYS Fluent. For turbulence, a RANS approach was adopted with the Reboud’s correction of turbulent viscosity in the k-ω SST model. Cavitation erosion was predicted with the Schenke-Melissaris-Terwisga (SMT) model, while particle erosion was predicted with the Det Norske Veritas (DNV) model. Two distinct erosion zones were identified, one for pure cavitation erosion and one for pure particle erosion. The occurrence of the pure particle erosion zone downstream of the cavitation erosion zone was analysed. By observing the streamlines downstream of the cavitation structures, it was found that vortices form in the flow and redirect the particles towards the wall, causing a pure particle erosion zone on the wall. Particles under consideration in this study were not found to alter the flow to the extent that the cavitation erosion zone would be significantly altered compared with the results without solid particles which are reported in the literature.
Ključne besede: cavitation, Particles ANSYS Fluent, erosion, CFD, modelling, DPM
Objavljeno v DKUM: 30.10.2023; Ogledov: 172; Prenosov: 7
.pdf Celotno besedilo (2,04 MB)
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Gonilni mehanizmi kavitacijskega vrtinca v vstopnem vodu radialne črpalke
Andrej Predin, Ignacijo Biluš, 2001, izvirni znanstveni članek

Opis: V prispevku je podana analiza gonilnih mehanizmov in tlačnih utripanj povezanih s pojavom kavitacijskega vrtinca v vstopnem vodu radialne črpalke. Kavitacijski vrtinec je rezultat interakcije številnih zapletenih sekundarnih tokovnih pojavov, ki nastopijo kot posledica obratovanja s podoptimalnimi pretoki v kavitacijskem obratovalnem režimu. Izvedene in predstavljene so tudi meritve tlačnih utripanj v vstopnem vodu radialne črpalke na različnih razdaljah od rotorskega ustja na sklenjeni kavitacijski merilni progi. Meritve so izvedene pri različnih vrtilnih hitrostih in različnih tlakih nad spodnjo vodno gladino. Podani so tudi rezultat frekvenčne analize posnetih tlačnih utripanj.
Ključne besede: radial pumps, cavitation, swirl, operating regime, pressure pulsation measurements
Objavljeno v DKUM: 10.07.2015; Ogledov: 1274; Prenosov: 24
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Experimental analysis of the impact of particles on the cavitating flow
Boštjan Gregorc, Andrej Predin, Drago Fabijan, Roman Klasinc, 2012, izvirni znanstveni članek

Opis: The purpose of this paper is to present an analysis of the impact of solid particles on the development of cavitating flow conditions around a hydrofoil. Experimental studies have been conducted in a cavitation tunnel with three different mixtures of particles and water. We used a particle-like properties, such as are found in river water, and with increasing mass concentration. We performed measurements of torque and the relative noise in the hydrofoil. The point in the formation of vapour phase on the hydrofoil and the pronounced frequency effect were determined by measuring the relative noise. Based on the analysis the results show that the particles increase the intensity and extent of cavitation.
Ključne besede: particles, cavitation, noise, measurements
Objavljeno v DKUM: 10.07.2015; Ogledov: 5845; Prenosov: 90
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