1. A novel pseudo-rigid body approach to the non-linear dynamics of soft micro-particles in dilute viscous flowJana Wedel, Matjaž Hriberšek, Jure Ravnik, Paul Steinmann, 2024, izvirni znanstveni članek Opis: We propose a novel, demonstrably effective, utmost versatile and computationally highly efficient
pseudo-rigid body approach for tracking the barycenter and shape dynamics of soft, i.e. nonlinearly deformable micro-particles dilutely suspended in viscous flow. Pseudo-rigid bodies are
characterized by affine deformation and thus represent a first-order extension to the kinematics
of rigid bodies. Soft particles in viscous flow are ubiquitous in nature and sciences, prominent
examples, among others, are cells, vesicles or bacteria. Typically, soft particles deform severely
due to the mechanical loads exerted by the fluid flow. Since the shape dynamics of a soft particle -
a terminology that shall here also include its orientation dynamics - also affects its barycenter
dynamics, the resulting particle trajectory as a consequence is markedly altered as compared to
a rigid particle. Here, we consider soft micro-particles of initially spherical shape that affinely
deform into an ellipsoidal shape. These kinematic conditions are commensurate with i) the affine
deformation assumption inherent to a pseudo-rigid body and ii) the celebrated Jeffery-Roscoe
model for the traction exerted on an ellipsoidal particle due to creeping flow conditions around
the particle. Without loss of generality, we here focus on non-linear hyperelastic particles for the
sake of demonstration. Our novel numerical approach proves to accurately capture the particular
deformation pattern of soft particles in viscous flow, such as for example tank-treading, thereby
being completely general regarding the flow conditions at the macro-scale and, as an option, the
constitutive behavior of the particle. Moreover, our computational method is highly efficient and
allows straightforward integration into established Lagrangian tracking algorithms as employed
for the point-particle approach to track rigid particles in dilute viscous flow.
Ključne besede: soft particles, pseudo-rigid bodies, Barycenter and shape dynamics, Lagrangian particle tracking
Objavljeno v DKUM: 19.09.2024; Ogledov: 0; Prenosov: 2
 Celotno besedilo (2,18 MB)
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2. A coupled point particle two-phase heat and mass transfer model for dispersed flows based on Boundary Element MethodsTimi Gomboc, Matej Zadravec, Jure Ravnik, Matjaž Hriberšek, 2024, objavljeni znanstveni prispevek na konferenci Opis: In dispersed multiphase flow processes we encounter coupled heat, mass and momentum transfer between the disoersed and the continuous phase. In the context of the subdomain Boundary Domain Integral Method (BDIM) solution of the Navier-Stokes equations a two-way coupling model is presented based on the use of the elliptic fundamental solution and the Dirac delta function properties which leads to accurate evaluation of the heat and mass point particle source impacts on the continuous (air) phase. In addition, the two-phase flow case under consideration is extended to the case of porous spherical particle drying with internal moving drying front, which is solved by the Boundary Element Method (BEM).
Ključne besede: heat transfer, mass transfer, Boundary Element Methods
Objavljeno v DKUM: 01.07.2024; Ogledov: 113; Prenosov: 11
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3. Analiza uporabe nanotekočin v toplotnih prenosnikih : magistrsko deloAndrej Špiler, 2024, magistrsko delo Opis: V magistrskem delu je obravnavana simulacija toplotnega prenosnika v krožni zanki, v katerem je nanotekočina. Nanotekočina je stabilna suspenzija majhnih delcev v nosilni tekočini. V magistrskem delu je nosilni medij voda, v kateri so nanodelci Al2O3. Simulacija se je izvedla v programskem paketu Ansys Fluent. Geometrija toplotnega prenosnika je bila narejena po toplotnem prenosniku, uporabljenem pri eksperimentu, ki sta ga izvedla Cobanoglu in Haktan Karadeniz v delu ''Effect of nanofluic thermophysical propertis on the performance prediciton of single-phase natural ciculation loops'' [1]. Za opis snovnih lastnosti nanotekočin, ki so temperaturno in koncentracijsko odvisne, se je uporabil UDF (User Defined Function). Gibanje in obnašanje nanodelcev v tekočini se je v programski paket Ansys Fluent vstavilo kot UDS (User defined Scalar). Rezultati cevi premera 4,75 mm so se primerjali z rezultati iz eksperimenta [1] pri toplotnih močeh 10, 30 in 50 W. Naknadno so se naredile simulacije za premere 3, 4, 5 in 6 mm ter pregledal se je izkoristek glede na večanje koncentracije nanodelcev. Rezultati so pokazali, da se z višanjem koncentracije nanodelcev veča izkoristek toplotnega prenosnika in manjša hitrost tekočine.
Ključne besede: prenos toplote, toplotni prenosniki, nanodelci, nanotekočine, Ansys Fluent, UDF, UDS
Objavljeno v DKUM: 03.04.2024; Ogledov: 253; Prenosov: 39
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4. Numerical simulations of the flow and aerosol dispersion in a violent expiratory event : Outcomes of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory eventsJordi Pallares, Alexandre Fabregat Tomas, Akim Lavrinenko, Hadifathul Akmal bin Norshamsudin, Gabor Janiga, David Frederick Fletcher, Kiao Inthavong, Marina Zasimova, Vladimir Ris, Nikolay Ivanov, Robert Castilla, Pedro Javier Gamez-Montero, Gustavo Raush, Hadrien Calmet, Daniel Mira, Jana Wedel, Mitja Štrakl, Jure Ravnik, Douglas Hector Fontes, Francisco José De Souza, Cristian Marchioli, Salvatore Cito, 2023, izvirni znanstveni članek Opis: This paper presents and discusses the results of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory events” aimed at assessing the ability of different computational codes and turbulence models to reproduce the flow generated by a rapid prototypical exhalation and the dispersion of the aerosol cloud it produces. Given a common flow configuration, a total of 7 research teams from different countries have performed a total of 11 numerical simulations of the flow dispersion by solving the Unsteady Reynolds Averaged Navier–Stokes (URANS) or using the Large-Eddy Simulations (LES) or hybrid (URANS-LES) techniques. The results of each team have been compared with each other and assessed against a Direct Numerical Simulation (DNS) of the exact same flow. The DNS results are used as reference solution to determine the deviation of each modeling approach. The dispersion of both evaporative and non-evaporative particle clouds has been considered in 12 simulations using URANS and LES. Most of the models predict reasonably well the shape and the horizontal and vertical ranges of the buoyant thermal cloud generated by the warm exhalation into an initially quiescent colder ambient. However, the vertical turbulent mixing is generally underpredicted, especially by the URANS-based simulations, independently of the specific turbulence model used (and only to a lesser extent by LES). In comparison to DNS, both approaches are found to overpredict the horizontal range covered by the small particle cloud that tends to remain afloat within the thermal cloud well after the flow injection has ceased.
Ključne besede: numerical simulations, computational fluid dynamics
Objavljeno v DKUM: 28.03.2024; Ogledov: 456; Prenosov: 453
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5. A point particle source model for conjugate heat and mass transfer in dispersed two-phase flows by BEM based methodsTimi Gomboc, Jurij Iljaž, Jure Ravnik, Matjaž Hriberšek, 2023, izvirni znanstveni članek Ključne besede: boundary-domain integral method, dispersed two-phase flow, two-way coupling, spherical porous particles, drying
Objavljeno v DKUM: 28.03.2024; Ogledov: 217; Prenosov: 17
Celotno besedilo (1,81 MB)
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6. A novel particle–particle and particle–wall collision model for superellipsoidal particlesJana Wedel, Mitja Štrakl, Matjaž Hriberšek, Paul Steinmann, Jure Ravnik, 2023, izvirni znanstveni članek Ključne besede: multiphase flow, Lagrangian particle tracking, superellipsoid, collision, friction
Objavljeno v DKUM: 28.03.2024; Ogledov: 171; Prenosov: 9
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7. Coefficient of tangential restitution for non-spherical particlesJana Wedel, Matjaž Hriberšek, Paul Steinmann, Jure Ravnik, 2024, izvirni znanstveni članek Opis: In various industrial and naturally occurring multiphase flows, whether dilute or dense, particle interaction plays a crucial role. In most cases, the particles are non-spherical, which poses a computational challenge in terms of particle motion and particle interaction, i.e. both particle–particle and particle–wall collisions. In this study, we present a novel frictional particle collision model to be used in general fluid flows. The model is derived for superellipsoidal particle shapes and thus allows consideration of frictional collisions of a wide variety of particle geometries. In this context, we derive an expression for the tangential coefficient of restitution applicable to arbitrarily shaped particles. Furthermore, we present the performance of the novel model by applying it to demonstrative examples ranging from two- to multi-particle systems.
Ključne besede: non-spherical particles, particle collision, tangential restitution coefficient, superellipsoids
Objavljeno v DKUM: 26.02.2024; Ogledov: 293; Prenosov: 23
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8. Development of an experimental Dead-End microfiltration layout and process repeatability analysisGorazd Bombek, Luka Kevorkijan, Grega Hrovat, Drago Kuzman, Aleks Kapun, Jure Ravnik, Matjaž Hriberšek, Aleš Hribernik, 2024, izvirni znanstveni članek Opis: Microfiltration is an important process in the pharmaceutical industry. Filter selection and validation is a time-consuming and expensive process. Quality by design approach is important for product safety. The article covers the instrumentalization and process control of a laboratory-scale dead-end microfiltration layout. The layout is a downscale model of the actual production line, and the goal is filter validation and analysis of process parameters, which may influence filter operation. Filter size, fluid pressure, valve plunger speed, and timing issues were considered. The focus is on the identification of the most influential process parameters and their influence on the repeatability of pressure oscillations caused by valve opening. The goal was to find the worst-case scenario regarding pressure oscillations and, consequently, filter energy intake. The layout was designed as compact as possible to reduce pressure losses between the filter and valve. Valve-induced pressure oscillations proved to be prevailing over the water hammer effect. Several filters in sizes between 3.5 cm2 and 6900 cm2 were tested, and some recommendations were suggested for the reduction of energy intake of the filter and to improve the repeatability of the process.
Ključne besede: filtration, pressure oscillations, repeatability, processes, parameters
Objavljeno v DKUM: 01.02.2024; Ogledov: 425; Prenosov: 22
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9. Numerical modeling of two-phase flow inside a wet flue gas absorber sumpNejc Vovk, Jure Ravnik, 2023, izvirni znanstveni članek Opis: A numerical model of a flue gas scrubber sump is developed with the aim of enabling optimization of the design of the sump in order to reduce energy consumption. In this model, the multiphase flow of the continuous phase, i.e., water, and the dispersed phase, i.e., air bubbles, is considered. The air that is blown in front of the agitators, as well as the influence of the flow field of the agitators on the distribution of the dispersed phase and the recirculation pumps as outlet, is modeled. The bubble Sauter mean diameter is modeled using the population balance model. The model is used to analyze operating parameters such as the bubble retention time, the average air volume fraction, bubble Sauter mean diameter, the local distribution of the bubble size and the amount of air escaping from the pump outlets at two operating points. The purpose of the model is to simulate the two-phase flow in the sump of the flue gas scrubber using air dispersion technology with a combination of spargers and agitators, which, when optimized, reduces energy consumption by 33%. The results show that the homogeneity of air is lower in the bottom part of the absorber sump and that the amount of air escaping through recirculation pipes equals 1.2% of the total air blown into the absorber sump. The escaping air consists mainly of bubbles smaller than 6 mm. Additional operating point results show that halving the magnitude of the linear momentum source lowers the air retention, as well as the average homogeneity of the dispersed air
Ključne besede: flue gas scrubbing, air dispersion, numerical model, OpenFoam
Objavljeno v DKUM: 19.12.2023; Ogledov: 359; Prenosov: 26
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10. Modelling of downscale model design and parameters for filter validation extention : zaključno poročiloMatjaž Hriberšek, Jure Ravnik, Aleš Hribernik, Jurij Iljaž, Matjaž Ramšak, Matej Zadravec, Gorazd Bombek, Timi Gomboc, 2023, končno poročilo o rezultatih raziskav Ključne besede: mechanics, porous materials, hydraulic model, mechanical properties
Objavljeno v DKUM: 03.11.2023; Ogledov: 653; Prenosov: 11 |
