191 results found
Hausmann M, Evrard F, van Wachem B, 2022, An efficient model for subgrid-scale velocity enrichment for large-eddy simulations of turbulent flows, PHYSICS OF FLUIDS, Vol: 34, ISSN: 1070-6631
Schenke S, Sewerin F, van Wachem B, et al., 2022, Acoustic black hole analogy to analyze nonlinear acoustic wave dynamics in accelerating flow fields, PHYSICS OF FLUIDS, Vol: 34, ISSN: 1070-6631
Denner F, Evrard F, van Wachem B, 2022, Breaching the capillary time-step constraint using a coupled VOF method with implicit surface tension, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 459, ISSN: 0021-9991
Schenke S, Sewerin F, van Wachem B, et al., 2022, Explicit predictor-corrector method for nonlinear acoustic waves excited by a moving wave emitting boundary, JOURNAL OF SOUND AND VIBRATION, Vol: 527, ISSN: 0022-460X
Schiodt M, Hodzic A, Evrard F, et al., 2022, Characterizing Lagrangian particle dynamics in decaying homogeneous isotropic turbulence using proper orthogonal decomposition, PHYSICS OF FLUIDS, Vol: 34, ISSN: 1070-6631
Schiødt M, Hodžić A, Evrard F, et al., 2022, Characterizing Lagrangian particle dynamics in decaying homogeneous isotropic turbulence using proper orthogonal decomposition, Physics of Fluids, Vol: 34, Pages: 063303-063303, ISSN: 1070-6631
<jats:p> Particle proper orthogonal decomposition (PPOD) is demonstrated as a method for extraction of temporal statistical information on dispersed (discrete) phases of multiphase flows. PPOD is an extension of the classical Eulerian POD, differentiating itself by its Lagrangian formulation and applicability to discrete phases in both stationary and non-stationary flows. The method is demonstrated on a test case of decaying homogeneous isotropic turbulence, where particle data are generated by one-way coupled simulations. Here, particle positions and velocities are integrated forward in time in a Lagrangian manner. The results demonstrate a proof of concept of the PPOD, and its potential for applicability. It is demonstrated that PPOD modes are able to capture both large scale temporal flow features as well as smaller scale variations. Additionally, particle trajectories/velocities are approximated using a subset of the PPOD basis where convergence is demonstrated. In the application of PPOD on multiple particle realizations, an increase in the convergence rate is observed as the initial particle separation is decreased. When decomposing both solid (rigid) and fluid particle velocities, the method provides the possibility of modal analysis of fluid–particle interactions in multiphase flows. For various configurations of rigid particle densities, the modal parallelity between the two phases is mapped, revealing a higher parallelity when the rigid particles are neutrally buoyant. </jats:p>
Gorges C, Evrard F, van Wachem B, et al., 2022, Reducing volume and shape errors in front tracking by divergence-preserving velocity interpolation and parabolic fit vertex positioning, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 457, ISSN: 0021-9991
Tawfik M, Zhang X, Grigartzik L, et al., 2021, Gene therapy with caspase-3 small interfering RNA-nanoparticles is neuroprotective after optic nerve damage, NEURAL REGENERATION RESEARCH, Vol: 16, Pages: 2534-+, ISSN: 1673-5374
Denner F, Evrard F, Castrejon-Pita AA, et al., 2021, Reversal and Inversion of Capillary Jet Breakup at Large Excitation Amplitudes, FLOW TURBULENCE AND COMBUSTION, Vol: 108, Pages: 843-863, ISSN: 1386-6184
Cerqueira RFL, Paladino EE, Evrard F, et al., 2021, Multiscale modeling and validation of the flow around Taylor bubbles surrounded with small dispersed bubbles using a coupled VOF-DBM approach, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 141, ISSN: 0301-9322
Ren Z, Liu S, Tan BH, et al., 2021, Strong shear flows release gaseous nuclei from surface micro- and nanobubbles, PHYSICAL REVIEW FLUIDS, Vol: 6, ISSN: 2469-990X
Reichl U, Seidel-Morgenstern A, Sundmacher K, et al., 2021, Research at the institute of process engineering at Otto von Guericke University Magdeburg, Chemie Ingenieur Technik - CIT, Vol: 93, Pages: 345-352, ISSN: 0009-286X
Seit der Gründung der Otto‐von‐Guericke‐Universität Magdeburg (OVGU) wurde der Forschungsbereich Verfahrenstechnik dort stetig ausgebaut. Heute umfasst die Fakultät für Verfahrens‐ und Systemtechnik der OVGU die vier Institute Verfahrenstechnik, Chemie, Strömungstechnik und Thermodynamik sowie Apparate‐ und Umwelttechnik. In diesem Beitrag stellen die fünf Lehrstühle des Instituts für Verfahrenstechnik (Bioprozesstechnik, Chemische Verfahrenstechnik, Systemverfahrenstechnik, Thermische Verfahrenstechnik und Mechanische Verfahrenstechnik) ihre Forschungsaktivitäten anhand ausgewählter Projekte vor.
Evrard F, Denner F, van Wachem B, 2021, Quantifying the errors of the particle-source-in-cell Euler-Lagrange method, International Journal of Multiphase Flow, Vol: 135, Pages: 1-6, ISSN: 0301-9322
The particle-source-in-cell Euler-Lagrange (PSIC-EL) method is widely used to simulate flows laden with particles. Its accuracy, however, is known to deteriorate as the ratio between the particle diameter ( d p ) and the mesh spacing ( h) increases, due to the impact of the momentum that is fed back to the flow by the Lagrangian particles. Although the community typically recommends particle diameters to be at least an order of magnitude smaller than the mesh spacing, the errors corresponding to a given d p /h ratio and/or flow regime have not been systematically studied. In this paper, we provide an expression to estimate the magnitude of the flow velocity disturbance resulting from the transport of a particle in the PSIC-EL framework, based on the d p /h ratio and the particle Reynolds number, Re p . This, in turn, directly relates to the error in the estimation of the undisturbed velocity, and therefore to the error in the prediction of the particle motion. We show that the upper bound of the relative error in the estimation of the undisturbed velocity, for all particle Reynolds numbers, is approximated by (6 / 5 ) d p /h . Moreover, for all cases where d p /h 1 / 2 , the expression we provide accurately estimates the value of the errors across a range of particle Reynolds numbers that are relevant to most gas-solid flow applications ( Re p < 500 ).
van Wachem B, Thalberg K, Duy N, et al., 2020, Analysis, modelling and simulation of the fragmentation of agglomerates, CHEMICAL ENGINEERING SCIENCE, Vol: 227, ISSN: 0009-2509
Evrard F, Denner F, van Wachem B, 2020, Euler-Lagrange modelling of dilute particle-laden flows with arbitrary particle-size to mesh-spacing ratio, Journal of Computational Physics: X, Vol: 8
This paper addresses the two-way coupled Euler-Lagrange modelling of dilute particle-laden flows, with arbitrary particle-size to mesh-spacing ratio. Two-way coupled Euler-Lagrange methods classically require particles to be much smaller than the computational mesh cells for them to be accurately tracked. Particles that do not satisfy this requirement can be considered by introducing a source term regularisation operator that typically consists in convoluting the point-wise particle momentum sources with a smooth kernel. Particles that are larger than the mesh cells, however, generate a significant local flow disturbance, which, in turn, results in poor estimates of the fluid forces acting on them. To circumvent this issue, this paper proposes a new framework to recover the local undisturbed velocity at the location of a given particle, that is the local flow velocity from which the disturbance due to the presence of the particle is subtracted. It relies upon the solution of the Stokes flow through a regularised momentum source and is extended to finite Reynolds numbers based on the Oseen flow solution. Owing to the polynomial nature of the regularisation kernel considered in this paper, a correction for the averaged local flow disturbance can be analytically derived, allowing to filter out scales of the flow motion that are smaller than the particle, which should not be taken into account to compute the interaction/drag forces acting on the particle. The proposed correction scheme is applied to the simulation of a particle settling under the influence of gravity, for varying particle-size to mesh-spacing ratios and varying Reynolds numbers. The method is shown to nearly eliminate any impact of the underlying mesh resolution on the modelling of a particle's trajectory. Finally, optimal values for the scale of the regularisation kernel are provided and their impact on the flow is discussed.
Liu D, Song J, Ma J, et al., 2020, Gas flow distribution and solid dynamics in a thin rectangular pressurized fluidized bed using CFD-DEM simulation, POWDER TECHNOLOGY, Vol: 373, Pages: 369-383, ISSN: 0032-5910
Shen L, Denner F, Morgan N, et al., 2020, Transient structures in rupturing thin-films: Marangoni-induced symmetry-breaking pattern formation in viscous fluids, Science Advances, Vol: 6, ISSN: 2375-2548
In the minutes immediately preceeding the rupture of a soap bubble,distinctive and repeatable patterns can be observed. These quasi-stabletransient structures are associated with the instabilities of the complexMarangoni flows on the curved thin film in the presence of a surfactantsolution. Here, we report a generalised Cahn-Hilliard-Swift-Hohenberg modelderived using asymptotic theory which describes the quasi-elastic wrinklingpattern formation and the consequent coarsening dynamics in a curvedsurfactant-laden thin film. By testing the theory against experiments on soapbubbles, we find quantitative agreement with the analytical predictions of thenucleation and the early coarsening phases associated with the patterns. Ourfindings provide fundamental physical understanding that can be used to(de-)stabilise thin films in the presence of surfactants and have importantimplications for both natural and industrial contexts, such as the productionof thin coating films, foams, emulsions and sprays.
Evrard F, Denner F, van Wachem B, 2020, Height-function curvature estimation with arbitrary order on non-uniform Cartesian grids, Journal of Computational Physics: X, Vol: 7
This paper proposes a height-function algorithm to estimate the curvature of two-dimensional curves and three-dimensional surfaces that are defined implicitly on two- and three-dimensional non-uniform Cartesian grids. It relies on the reconstruction of local heights, onto which polynomial height-functions are fitted. The algorithm produces curvature estimates of order N−1 anywhere in a stencil of (N+1)d−1 heights computed from the volume-fraction data available on a d-dimensional non-uniform Cartesian grid. These estimates are of order N at the centre of the stencil when it is symmetric about its main axis. This is confirmed by a comprehensive convergence analysis conducted on the errors associated with the application of the algorithm to a fabricated test-curve and test-surface.
Denner F, Evrard F, van Wachem B, 2020, Modeling Acoustic Cavitation Using a Pressure-Based Algorithm for Polytropic Fluids, FLUIDS, Vol: 5
Lukas E, Roloff C, van Wachem B, et al., 2020, Experimental investigation of the grade efficiency of a zigzag separator, Powder Technology, Vol: 369, Pages: 38-52, ISSN: 0032-5910
An experimental study is conducted on a pilot-scale zigzag air separator (ZZS) to study the effects of varying the solid feed mass stream, the mean channel air velocity, and the number of channel segments onto the grade efficiency. Spherical glass beads are classified. A straight pipe separator model (PSM) is modified for the ZZS and fitted to the experimental data to estimate the relative cut-point settling velocity, the separation sharpness, the relative rise velocity, the diffusion coefficient, and the particle loading. The proposed model is thoroughly investigated with regard to all important parameters, e.g. the estimated particle loading is shown to be more precise than the ratio of the solid and air mass stream, used in many publications. Finally, the relative rise velocity is shown to be only a function of the particle loading, making the experimental results within the model collapse.
Denner F, Evrard F, van Wachem BGM, 2020, Conservative finite-volume framework and pressure-based algorithm for flows of incompressible, ideal-gas and real-gas fluids at all speeds, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 409, ISSN: 0021-9991
van Wachem B, Curran T, Evrard F, 2020, Fully Correlated Stochastic Inter-Particle Collision Model for Euler-Lagrange Gas-Solid Flows, FLOW TURBULENCE AND COMBUSTION, Vol: 105, Pages: 935-963, ISSN: 1386-6184
Lukas E, Roloff C, Mann H, et al., 2020, Experimental study and modelling of particle behaviour in a multi-stage zigzag air classifier, Dynamic Flowsheet Simulation of Solids Processes, Pages: 391-410, ISBN: 9783030451677
In most industrial solid processing operations, the classification of particles is important and designed based on the terminal settling velocity as the main control parameter. This settling velocity is dependent on characteristic particle properties like size, density, and shape. Turbulent particle diffusion is the other key property controlling the efficiency of the separation. In this project, multi-stage separation experiments of a variety ofmaterials have been performed using different flow velocities, mass loadings of the air, number of stages. Separation has been investigated separately concerning particle size, particle density, and particle shape. Continuous operation in terms of solid material and airflow has been mostly considered. However, variations in mass loading and pulsating operation of the fan have been investigated as well. The performance has been analyzed and discussed with respect to the separation functions, for instance regarding separation sharpness. Severalmodelling approaches have been checked and/or developed to describe theoretically the corresponding observations. After fitting the free model parameters, a very good agreement has been obtained compared to experimental measurements. Finally, the reduced model has been implemented into the central software DYSSOL.
Knight C, O'Sullivan C, Dini D, et al., 2020, Computing drag and interactions between fluid and polydisperse particles in saturated granular materials, Computers and Geotechnics, Vol: 117, Pages: 1-16, ISSN: 0266-352X
Fundamental numerical studies of seepage induced geotechnical instabilities and filtration processes depends on accurate prediction of the forces imparted on the soil grains by the permeating fluid. Hitherto coupled Discrete Element Method (DEM) simulations documented in geomechanics have most often simulated the fluid flow using computational fluid dynamics (CFD) models employing fluid cells that contain a number of particles. Empirical drag models are used to predict the fluid-particle interaction forces using the flow Reynolds number and fluid cell porosity. Experimental verification of the forces predicted by these models at the particle-scale is non-trivial. This contribution uses a high resolution immersed boundary method to model the fluid flow within individual voids in polydisperse samples of spheres to accurately determine the fluid-particle interaction forces. The existing drag models are shown to poorly capture the forces on individual particles in the samples for flow with low Reynolds number values. An alternative approach is proposed in which a radical Voronoi tesselation is applied to estimate a local solids volume fraction for each particle; this local solids fraction can be adopted in combination with existing expressions to estimate the drag force. This tessellation-based approach gives a more accurate prediction of the fluid particle interaction forces.
You Q, Sokolov M, Grigartzik L, et al., 2019, How Nanoparticle Physicochemical Parameters Affect Drug Delivery to Cells in the Retina via Systemic Interactions, MOLECULAR PHARMACEUTICS, Vol: 16, Pages: 5068-5075, ISSN: 1543-8384
Denner F, van Wachem BGM, 2019, Numerical modelling of shock-bubble interactions using a pressure-based algorithm without Riemann solvers, Experimental and Computational Multiphase Flow, Vol: 1, Pages: 271-285, ISSN: 2661-8869
The interaction of a shock wave with a bubble features in many engineering and emerging technological applications, and has been used widely to test new numerical methods for compressible interfacial flows. Recently, density-based algorithms with pressure-correction methods as well as fully-coupled pressure-based algorithms have been established as promising alternatives to classical density-based algorithms based on Riemann solvers. The current paper investigates the predictive accuracy of fully-coupled pressure-based algorithms without Riemann solvers in modelling the interaction of shock waves with one-dimensional and two-dimensional bubbles in gas-gas and liquid-gas flows. For a gas bubble suspended in another gas, the mesh resolution and the applied advection schemes are found to only have a minor influence on the bubble shape and position, as well as the behaviour of the dominant shock waves and rarefaction fans. For a gas bubble suspended in a liquid, however, the mesh resolution has a critical influence on the shape, the position and the post-shock evolution of the bubble, as well as the pressure and temperature distribution.
Pinheiro AP, Vedovoto JM, Neto ADS, et al., 2019, Ethanol droplet evaporation: Effects of ambient temperature, pressure and fuel vapor concentration, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, Vol: 143, ISSN: 0017-9310
Jebelisinaki F, Boettcher R, van Wachem B, et al., 2019, Impact of dominant elastic to elastic-plastic millimeter-sized metal spheres with glass plates, POWDER TECHNOLOGY, Vol: 356, Pages: 208-221, ISSN: 0032-5910
Evrard F, Denner F, van Wachem B, 2019, A multi-scale approach to simulate atomisation processes, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 119, Pages: 194-216, ISSN: 0301-9322
Marnani AK, Bueck A, Antonyuk S, et al., 2019, The Effect of Very Cohesive Ultra-Fine Particles in Mixtures on Compression, Consolidation, and Fluidization, PROCESSES, Vol: 7
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