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Development of CFD solver for four-way coupled particle-laden flows
Šourek, M. ; Isoz, Martin
Computational uid dynamics (CFD) simulations containing freely moving bodies are still a challenging topic. More so, if the bodies are large enough to a_ect the uid ow and distributed\ndensely enough to come in contact both with the boundaries of the computational domain and with each other. In this work, we concentrate on the topic of simulation of (i) irregular bodies\nwith ow-induced movement and contact with computational domain boundaries taken into account, and (ii) bodies entrained by the uid and coming in contact not only with the domain\nboundaries but also with each other. The developed modeling approach is based on the hybrid _ctitious domain-immersed boundary method extended by the discrete element method. The\npresent contribution is focused on presentation of simulation principles and results of initial benchmark cases.
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POD-DEIM-based model order reduction for four-way coupled fluid-solid flows
Isoz, Martin ; Šourek, M.
Proper orthogonal decomposition (POD) and discrete empirical interpolation method (DEIM) have become established tools for model order reduction in simulations of fluid flows. However, including moving solid bodies in the computational domain poses additional issues with respect to the fluid-solid coupling and to the solution of the movement of the solids. Still, it seems that if the hybrid ctitious domain-immersed boundary method is used to include the solids in the flow domain, POD-DEIM based approaches may be extended for four-way coupled particleladen flows. The present work focuses on the construction of POD-DEIM based reduced order models for the aforementioned flows.
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Geometrically realistic macro-scale model for multi-scalesimulations of catalytic filters for automotive gasaftertreatment
Hlavatý, Tomáš ; Isoz, Martin ; Plachá, M. ; Šourek, M. ; Kočí, P.
This paper is part of a research focused on simulating (i) the catalytic conversion of environment endangering gases, and (ii) trapping of the particulate matter in automotive exhaust gas aftertreatment. Historically, the catalytic conversion and the filtration of soot particles were performed in independent devices. However, recent trend is to combine the catalytic converter and soot filter into a single device, the catalytic filter. Compared to the standard two-device system, the catalytic filter is more compact and has lower heat losses. Nevertheless, it is highly sensitive to the catalyst distribution. This study extends our recently developed methodology for pore-scale simulations of flow, diffusion and reaction in the coated catalytic filters. The extension consists of enabling data transfer from macro- to pore-scale models by preparing geometrically realistic macro-scale CFD simulations. The simulation geometry is based on XRT scans of real-life catalytic filters. The flow data from the newly developed macro-scale model are mapped as boundary conditions into the pore-scale simulations and used to improve the estimates of the catalytic filter filtration efficiency.
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On the influence of diffusion stabilization in Oldroyd-B fluid flow simulations
Pires, M. ; Bodnár, Tomáš
This work presents some numerical tests of finite element solution of incompressible Oldroyd-B fluid flows. The effect of numerical stabilization using artificial stress diffusion is investigated in detail. The limits of Weissenberg number We for which it is possible to obtain the numerical solution were studied depending on the Reynolds number Re and the diffusion parameter. Series of numerical tests were performed for steady two-dimensional Oldroyd-B fluid flow in corrugated channel (tube). The numerical results clearly proved the advantage (higher attainable We) of stabilized numerical method over the classical formulation without the artificial stress diffusion.
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CFD Simulation of a Sub-millimetre Rising Bubble in a Stagnant Liquid.
Crha, Jakub ; Basařová, P. ; Kašpar, O.
Hydrodynamics of the multiphase apparatus is strongly affected by fluids used in the process. One of the main quantities, which determine the hydrodynamic behaviour is the rising velocity of gaseous bubbles. This velocity can be determined easily in small scale apparatuses, but it can be much more challenging in industrial-scale devices. For that reason, mathematical modeling is used. COMSOL Multiphysics, finite element CFD solver, was used to describe the behaviour of the single bubble rising in aqueous solutions of ethanol and n-propanol. Aqueous solutions of low-carbon alcohols are extensively used in many multiphase chemical processes such as distillation, flotation and in multiphase reactors. Bubble velocities and shapes obtained from the simulation were compared to experimental and theoretical values. Two initial diameters of bubbles were used – 0.6 and 0.8 mm. Terminal velocities and shapes deformations obtained from COMSOL of 0.6 mm bubble were in an agreement with theoretical and experimental values.
Plný tet:  PDF
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Laminar-Turbulent Transition in View of Flow Separation from Isothermal and Heated Cylinder
Pech, Jan
This work presents insight to the laminar-turbulent transition in flow around cylinder through a numerical simulation, both in isothermal and heated case. The flow is modelled directly as a solution to the Navier-Stokes and Navier-Stokes-Fourier system. Reynolds numbers are considered in range 100-20000, ratio of cylinder-wall and upstream temperature is up to 1.5. Curves representing evolution of separation positions in time provide novel insight to vortex formation. Various regimes are recognized and some of them can be assigned to phenomena described formerly in experiment.
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Recent results on the problem of motion of viscous fluid around a rotating rigid body
Deuring, P. ; Kračmar, Stanislav ; Nečasová, Šárka
We consider the linearized incompressible flow around rotating and translating body in the exterior domain R³D‾, where D⊂R³ is open and bounded, with Lipschitz boundary. We derive the pointwise estimates for the pressure. Further, we consider the linearized problem in a truncation domain DR:=BRD‾ of the exterior domain R³D‾ under certain artificial boundary conditions on the truncating boundary ∂BR, and then compare this solution with the solution in the exterior domain R³D‾ to get the truncation error estimate.
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Aeroacoustic simulation of human phonation with the wale sub-grid scale model
Šidlof, Petr ; Lasota, M.
The paper reports on an aeroacoustic model of voice generation in human larynx, based on Large Eddy Simulation with the Wall-Adapting Local Eddy-Viscosity (WALE) sub-grid scale (SGS) model. The simulation uses a three-step hybrid approach, with an incompressible finite volume CFD computation providing the filtered velocity and pressure, evaluation of the aeroacoustic sources, and simulation of the sound propagation by finite element discretization of the Acoustic Perturbation Equations. The WALE SGS model is used to overcome the limitation of the classical Smagorinski SGS model, which overpredicts the SGS viscosity in regions of high shear, especially within the boundary layer in the glottal constriction. Results of the 3D CFD simulation, location of the aeroacoustic sources and the spectra of the radiated sound for two vowels are presented.
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On the 3D Dynamics of the Wake Behind a Circular Cylinder
Uruba, Václav ; Procházka, Pavel P. ; Skála, Vladislav
Flow in the wake of a circular cylinder is studied experimentally using time-resolved stereo PIV method. Special attention is paid to 3D topology of dynamical structures. While the distribution of statistic quantities along the cylinder is uniform, and i.e. 2D, the instantaneous flow structure is fully 3D. Within the velocity fluctuating flow field the structures containing streamwise vorticity and velocity components are dominant. The POD modes connected with von Kármán vortex street are identified.
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