1. Cavitation erosion modelling : comparison of different driving pressure approachesLuka 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: 387; Downloads: 13
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2. Primerjava sistemov CAD (Solidworks in Onshape) pri 3D modeliranju : diplomsko deloJan Gabrijel, 2023, undergraduate thesis Abstract: Programska oprema za računalniško podprto konstruiranje je stalnica pri razvoju izdelkov in ima velik vpliv na različne tehnologije in sisteme proizvodnje v raznovrstnih panogah. Razvoj in uporaba teh sistemov je ključno spremenila tradicionalne metode razvoja izdelkov vse od prototipa do končne proizvodnje. Čeprav se teoretske metode modeliranja ne spreminjajo veliko, je njihov razvoj v zadnjem času predvsem usmerjen na prilagajanje vedno močnejši strojni opremi, kakovosti prikazovanja in predvsem soočanja s številnimi izzivi kot so dostopnost do skupnih podatkovnih baz, komunikacija preko računalniških mrež, težave z verzijami ter stroški strojne opreme in licenciranja.
Novejša programska oprema CAD v oblaku, uporabnikom ponuja novo in drugačno storitev, ki ne zahteva namestitve programske opreme in licenciranje, in je enostavno dosegljiva iz internetnega prikazovalnika. Programska oprema v oblaku na splošno sicer še ne odgovarja na vsa vprašanja, ki se ob pojavljajo ob uporabi, vendar že prinaša nove pristope, ki nakazujejo smernice drugačne uporabe sistemov CAD.
V diplomski nalogi smo na primeru geometrije sklopa parnega stroja primerjali sistema CAD: Solidwoks kot tradicionalni sistem CAD in Onshape kot primer sistema CAD v oblaku. Namen diplomske naloge je uporabniška izkušnja dveh programskih sistemov CAD na enakem izdelku katere rezultat so številni dejavniki, ki jih je potrebno upoštevati. Ugotovimo lahko, da je uporabniška izkušnja zelo podobna, a je prednost, ob zagotovljeni varnosti podatkov na strani oblačnih storitev.
Keywords: sistemi CAD, modeliranje, računalništvo v oblaku
Published in DKUM: 16.01.2024; Views: 376; Downloads: 19
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3. Lift and drag coefficients for different magnus rotor typesMarko Pezdevšek, 2019, original scientific article Abstract: In this paper, the results of numerical simulations for various Magnus rotor configurations are presented. For each configuration, a blocked structured mesh was designed in ICEM CFD. Numerical simulations were conducted using Ansys CFX. The influence of the aspect ratio on the lift and drag coefficients depending on the speed ratio was investigated, as was the influence of endplates on a Magnus rotor. From the obtained results, it was concluded that adding endplates to a Magnus rotor increases the lift and drag coefficients.
Keywords: Magnus effect, lift coefficient, drag coefficient, Ansys CFX, endplates, aspect ratio
Published in DKUM: 05.12.2023; Views: 399; Downloads: 6
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4. Influence of Numerical Mesh Type on Airfoil Aerodynamic CharacteristicsMarko Pezdevšek, Matej Fike, Andrej Predin, Gorazd Hren, 2019, published scientific conference contribution Abstract: In this paper, we will examine how different mesh types affect the aerodynamic characteristic of an airfoil. The airfoil used for this paper was the NREL S809. Three different mesh types were created, a blocked structured mesh, an unstructured mesh and a hybrid mesh containing a blocked structured mesh near the surface of the airfoil and an unstructured mesh on the outside perimeter. Steady state simulations were performed for angles of attack between 0°and 22°. Lift and drag coefficient for all created meshes were compared to experimental results from literature. From angles of attack between 2° and 8° all three meshes predict similar lift and drag coefficients. We encountered problems with convergence for the unstructured mesh at angles of attack higher than 8°. Structured and hybrid mesh had similar lift and drag coefficients across all angles of attack.
Keywords: computational fluid dynamics, NREL S809, structured mesh, unstructured mesh, hybrid mesh
Published in DKUM: 04.12.2023; Views: 346; Downloads: 18
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5. Experimental and Numerical Research of Micro Wind Turbine for Low Wind SpeedsMatej Fike, Marko Pezdevšek, Andrej Predin, Gorazd Hren, 2019, published scientific conference contribution Abstract: In this paper, experimental and numerical study of micro wind turbine for low wind speeds is presented. Numerical simulations were performed for two turbines with different blades at various wind speeds. The first geometry was NTNU turbine and the second was modified NTNU turbine with shorter blades. Results from the numerical study showed that more efficient with higher power coefficient is turbine with modified blades.
Keywords: wind turbine, NREL S826, CFD, power coefficient, structured mesh
Published in DKUM: 04.12.2023; Views: 297; Downloads: 20
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6. Lost Energy of Water Spilled over Hydropower DamsAndrej Predin, Matej Fike, Marko Pezdevšek, Gorazd Hren, 2021, original scientific article Abstract: The present paper presents a view of water spilled over hydropower plants as an energy loss. In the current climate conditions, flood events are becoming more frequent due to human impact on the environment; water spills are also more frequent, which means more and more energy is lost. How much water is spilled and, consequently, how much energy is lost is shown in the present article on the chain of power plants on the Sava River in the five years from 2015 to 2019. An analytical assessment of the current situation in the lock was carried out, which showed that the available water through the locks could be used efficiently. The paper presents a case study of one overflow event lasting 48 h. The calculated theoretical losses of energy (of spilled water) and possible technical implementation for capturing losses are given. The proposed technical implementation is based on established technology, so we could expect that the approach is feasible. The results show that the estimated spilled water energy potential reaches about 40% of the actual spilled water or energy lost.
Keywords: energy loss, spilled water energy, hydropower
Published in DKUM: 13.11.2023; Views: 261; Downloads: 15
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7. Comparison of cavitation models for the prediction of cavitation around a hydrofoilMarko Pezdevšek, Ignacijo Biluš, Gorazd Hren, 2021, original scientific article Abstract: 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.
Keywords: hydrofoil, cavitation, Ansys CFX
Published in DKUM: 10.11.2023; Views: 387; Downloads: 7
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10. Thermal analysis of a coreless axial flux permanent magnet machineFranjo Pranjić, Marko Pezdevšek, Peter Virtič, 2022, original scientific article Abstract: The article deals with numerical analysis of a double sided coreless axial flux permanent magnet machine with two rotor disks and a coreless stator. Coreless stator represents copper windings which are held together by epoxy raisin, therefore a special focus has to be given to the stator temperature. In this article a numerical analysis is presented, which is based on the copper losses, namely the I2R product, where the resistance of the copper windings was both calculated as well as measured in the prototype machine.
Keywords: axial flux, CFD, coreless, permanent magnet, temperature distribution
Published in DKUM: 27.10.2023; Views: 357; Downloads: 14
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