1. Reversible pump-turbines - a study of pumping mode off-design conditionsUroš 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: 25; Prenosov: 1
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2. Comparison of cavitation models for the prediction of cavitation around a hydrofoilMarko 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: 52; Prenosov: 4
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4. Prediction of cavitation and particle erosion in a radial divergent test sectionLuka 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: 56; Prenosov: 6
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5. Gonilni mehanizmi kavitacijskega vrtinca v vstopnem vodu radialne črpalkeAndrej 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: 1171; Prenosov: 24
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6. Experimental analysis of the impact of particles on the cavitating flowBoštjan 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: 5735; Prenosov: 88
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