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Simple Rheoscopic Flows Used in Teaching Fluid Mechanics
Duda, D.; Yanovych, Vitalii; Uruba, Václav
2022 - anglický
Four simple demonstration experiments are presented. They are used as a support in the teaching of Fluid Mechanics I (a compulsory lecture at the University of West Bohemia in Pilsen). All mentioned experiments use the rheoscopic fluid obtained as a water solution of mica powder to visualize the flow in a esthetic way, which, as we hope, has a potential to attract students attention. The experiments are: demonstration of Bernoulli equation in a widening and narrowing channel, Taylor-Couette flow, the effect of viscosity to the scales and decay of turbulence, and the Galilean transformation inside an axial compressor.
Klíčová slova:
teaching; fluid mechanics; demonstration experiment; rheoscopic fluid; Bernoulli equation; Taylor-Couette flow; axial compressor
Dokument je dostupný na externích webových stránkách.
Simple Rheoscopic Flows Used in Teaching Fluid Mechanics
Four simple demonstration experiments are presented. They are used as a support in the teaching of Fluid Mechanics I (a compulsory lecture at the University of West Bohemia in Pilsen). All mentioned ...
Effect of Cylinder Roughness on Strouhal Number
Yanovych, Vitalii; Duda, D.; Uruba, Václav; Procházka, Pavel P.; Antoš, Pavel
2022 - anglický
The main goal of this paper is to establish a better understanding of the relationship between a Strouhal number and surface roughness. Hot-wire anemometry was used to evaluations the characteristics of turbulent flow behind circular cylinders with different relative roughness 0% (smooth surface) 0.83%, 1.67%, 3.33%, and 6.67%. At the experimental investigation, the Reynolds number based on the cylinder diameter was 5 × 103 < Red < 2 × 104. The obtained data showed that the Strouhal number decreased with increasing roughness. While, the dissipation rate decreases, and the value of the Kolmogorov and Taylor microscales increases. Also, spectral analysis of streamwise velocity fluctuations allowed us to estimate the location of the vortex-shedding frequency which at growing roughness tends to reduce.
Klíčová slova:
roughened cylinder; Strouhal number; spectral distribution; turbulence structure; Hot-wire anemometry
Dokument je dostupný na externích webových stránkách.
Effect of Cylinder Roughness on Strouhal Number
The main goal of this paper is to establish a better understanding of the relationship between a Strouhal number and surface roughness. Hot-wire anemometry was used to evaluations the characteristics ...
A parallel algorithm for flux-based bounded scalar Re-distribution
Isoz, Martin; Plachá, M.
2022 - anglický
Let us assume a bounded scalar function ? : Q = I × ? ? ?0, 1?, I ? R, ? ? R3, where Q is an open bounded domain and its discrete counterpart ?h defined on a computational mesh Qh = Ih × ?h. The problem of redistribution of ?h over ?h ensuring the scalar boundedness while maintaining the invariance of R ?h ?h dV is surprisingly frequent within the field of computational fluid dynamics (CFD). The present contribution is motivated by the case arising from coupling Lagrangian particle tracking and particle deposition within ? h with Eulerian CFD computation. We propose an algorithm for ?h redistribution that is (i) based on fluxes over the computational cells faces, i.e. suitable for finite volume (FV) computations, (ii) localized, meaning that a cell ?h P with ?hP > 1 affects only its closest neighbors with ?h < 1, and (iii) designed for parallel computations leveraging the standard domain decomposition methods.
Klíčová slova:
CFD; OpenFOAM; scalar redistribution
Dokument je dostupný na externích webových stránkách.
A parallel algorithm for flux-based bounded scalar Re-distribution
Let us assume a bounded scalar function ? : Q = I × ? ? ?0, 1?, I ? R, ? ? R3, where Q is an open bounded domain and its discrete counterpart ?h defined on a computational mesh Qh = Ih × ?h. The ...
Octree-generated virtual mesh for improved contact resolution in CFD-Dem coupling
Studeník, O.; Kotouč Šourek, M.; Isoz, Martin
2022 - anglický
The present work is focused on improving the efficiency of a computational fluid dynamics (CFD) – discrete element method (DEM) solver allowing for computations with non-spherical solids. In general, the combination of CFD and DEM allows for simulations of freely moving solid particles within a computational domain containing fluid. The standard approach of CFD-DEM solvers is to approximate solid bodies by spheres, the geometry of which can be fully defined via its radius and center position. Consequently, the standard DEM contact models are based on an overlap depth between particles, which can be easily evaluated for a sphere-sphere contact. However, for a contact between two non-spherical particles, the overlap depth cannot be used and has to be replaced by the more general overlap volume. The precision of the overlap volume computation is (i) crucial for the correct evaluation of contact forces, and (ii) directly dependent on the computational mesh resolution. Still, the contact volume evaluation in DEM for arbitrarily shaped bodies is usually by at least one order of magnitude more demanding on the mesh resolution than the CFD. In order to improve the computational efficiency of our CFD-DEM solver, we introduce the concept of an OCTREEbased virtual mesh, in which the DEM spatial discretization is adaptively refined while the CFD mesh remains unchanged.
Klíčová slova:
HFDIB-DEM; CFD; DEM; washcoating; OpenFOAM
Dokument je dostupný na externích webových stránkách.
Octree-generated virtual mesh for improved contact resolution in CFD-Dem coupling
The present work is focused on improving the efficiency of a computational fluid dynamics (CFD) – discrete element method (DEM) solver allowing for computations with non-spherical solids. In general, ...
The Design and Aerodynamic Testing of DPIK Probe
Procházka, Pavel P.; Barraclough, V.; Skála, Vladislav; Uruba, Václav
2022 - anglický
The isokinetic probe used to detect the liquid phase drift from the cooling tower is presented here. The main motivation is costs reduction that arises during standard drift measurements. The probe was developed in the framework of the grant project between private company 4Jtech and Institute of Thermomechanics. The aerodynamic design and optimization of this probe should fulfill one important criterion – to capture the droplets from the drift with maximal efficiency. Kalorimetric principle is then used to evaluate the amount of trapped water. Standard PIV (Particle Image Velocimetry) measurement technique and modified IPI (Interferometric Particle Imaging) methods were used to measure the flow field topology and the particle size distribution, respectively.
Klíčová slova:
isokinetic probe; cooling tower; PIV; droplet size
Dokument je dostupný na externích webových stránkách.
The Design and Aerodynamic Testing of DPIK Probe
The isokinetic probe used to detect the liquid phase drift from the cooling tower is presented here. The main motivation is costs reduction that arises during standard drift measurements. The probe ...
Investigation of Transonic Flow through Linear Cascade with Single Blade Incidence Angle Offset
Fürst, J.; Musil, Josef; Šimurda, David
2022 - anglický
The contribution deals with numerical and experimental investigation of the effect of incidence angle offset in a two-dimensional section of a flat linear blade cascade in a high-speed wind tunnel. The aim of the work is to complement ongoing research of quasi-stationary approximation of aerodynamic flutter by examination of setups leading to transonic flow regimes. The numerical simulations were realized by finite-volume, in-house code developed on top of the open-source software package OpenFOAM. The experiments were conducted in correspondence with the setting of numerical simulations. The comparison of experimental and numerical data is presented on the isentropic Mach number distributions at various locations in the blade cascade. The description of transonic flow structures in the vicinity of blades is also provided.
Klíčová slova:
compressor cascade; flutter; CFD; finite volumes; experimental validation; transonic
Dokument je dostupný na externích webových stránkách.
Investigation of Transonic Flow through Linear Cascade with Single Blade Incidence Angle Offset
The contribution deals with numerical and experimental investigation of the effect of incidence angle offset in a two-dimensional section of a flat linear blade cascade in a high-speed wind tunnel. ...
Developing a coupled CFD solver for mass, momentum and heat transport in catalytic filters
Hlavatý, Tomáš; Isoz, Martin; Kočí, P.
2022 - anglický
Using catalytic filters (CF) in automotive exhaust gas aftertreatment decreases the system heat losses and facilitates the CF regeneration. On the other hand, the CF overall performance is strongly dependent on the catalytic material distribution within it. In the present work, we aim to provide a computational framework to study the dependence of the CF characteristics, i.e. the pressure loss and the conversion of gaseous pollutants, on the catalyst distribution. Previously, we built an isothermal computational fluid dynamics (CFD) model of the flow and conversion of gaseous pollutants inside the CF. However, the reactions occurring inside the CF are exothermic and the assumption of constant temperature proved to be too restricting for real-life applications of the developed isothermal CFD model. Thus, in this work, we extend the framework by the enthalpy balance, which requires combining all the transport equations (mass, momentum and enthalpy) in a single solver. The new and more general solver provides results in good agreement with a well established (1+1)D channel model calibrated on experimental data. Furthermore, it allows studying more complex device-scale geometries of laboratory CF samples.
Klíčová slova:
CFD; catalytic filter; OpenFOAM; gasoline particulate filter (GPF)
Dokument je dostupný na externích webových stránkách.
Developing a coupled CFD solver for mass, momentum and heat transport in catalytic filters
Using catalytic filters (CF) in automotive exhaust gas aftertreatment decreases the system heat losses and facilitates the CF regeneration. On the other hand, the CF overall performance is strongly ...
Estimating rheological properties of suspensions formed of arbitrarily-shaped particles via CDF-Dem
Kotouč Šourek, M.; Isoz, Martin
2022 - anglický
In recent years, new methods combining computational fluid dynamics (CFD) and discrete element method (DEM) have been intensively studied. Usually, these methods are focused on simulations of spherical particles. Nevertheless, this is inadequate for a simulation of a common suspension, the rheology of which is affected by particle shapes. In this work, we leverage the capabilities of an in-house developed CFD-DEM solver to simulate suspensions formed of arbitrarily-shaped particles. Specifically, we simulate a rheological measurement to estimate the suspension viscosity. The CFD-DEM estimates are in very good agreement with available experimental data and correlations proving the new solver capabilities regarding firstprinciples-based simulations of complex non-Newtonian suspension behaviour. The practical potential of suspension simulation is illustrated in a numerical study of the washcoating process in the preparation of a catalytic filter for automotive exhaust gas after-treatment.
Klíčová slova:
CFD-DEM; HFDIB; suspension rheology; OpenFOAM
Dokument je dostupný na externích webových stránkách.
Estimating rheological properties of suspensions formed of arbitrarily-shaped particles via CDF-Dem
In recent years, new methods combining computational fluid dynamics (CFD) and discrete element method (DEM) have been intensively studied. Usually, these methods are focused on simulations of ...
Hybrid fictitious domain-immersed boundary method in CFD-based topology optimization
Kubíčková, Lucie; Isoz, Martin
2022 - anglický
Advances in technological development, especially in 3D printing, allow engineers to design components with almost arbitrary shape and connectivity. Consequently, more and more attention is being directed towards a highly-specialized application-driven component design based on topology optimization (TO). In the present work, we propose a methodology enabling TO of components in contact with flowing fluids. In particular, the optimization itself is based on multi-objective evolutionary algorithms (MOEAs) with the component geometry encoded using a binary representation. The optimization criteria are evaluated via computational fluid dynamics (CFD). The main novelty of the proposed TO framework lies in its robustness and effectiveness achieved by utilizing a single computational mesh for all the tested designs and projecting the specific components shapes onto it by the means of an immersed boundary method. The new methodology capabilities are illustrated on a shape optimization of a diffuser equipped as a part of an ejector. The optimization goal was to increase the ejector energy efficiency. The newly proposed methodology was able to identify a design by roughly 9 % more efficient than an alternative one found utilizing a previously published and less general optimization approach.
Klíčová slova:
HFDIB; topology optimization; CFD; OpenFOAM
Dokument je dostupný na externích webových stránkách.
Hybrid fictitious domain-immersed boundary method in CFD-based topology optimization
Advances in technological development, especially in 3D printing, allow engineers to design components with almost arbitrary shape and connectivity. Consequently, more and more attention is being ...
Assessment of Various Converging Inlet Nozzles for Wind Tunnel Using CFD
Kosiak, Pavlo; Radnic, Tomáš; Mamula, Milan; Hála, Jindřich; Šimurda, David; Luxa, Martin
2022 - anglický
A new calibration tunnel intended for pressure probe calibration is being designed at the Aerodynamic Laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT CAS). A critical part of the design is the converging nozzle since it can substantially affect the resulting flow field in the test section. Three types of nozzles were chosen for the CFD investigation: two-sine, Vitoshinski, and Vagt. For each type of nozzle, two configurations were considered: long (645 mm) and short (353mm). Flow of the viscous, compressible fluid through all the variants was simulated using Ansys CFX commercial software. Results proved the Vagt nozzle to have the most uniform velocity profile and zero curvature at its end making it the most suitable for the intended use.
Klíčová slova:
CFD; ANSYS CFX; converging nozzle; wind tunnel design
Dokument je dostupný na externích webových stránkách.
Assessment of Various Converging Inlet Nozzles for Wind Tunnel Using CFD
A new calibration tunnel intended for pressure probe calibration is being designed at the Aerodynamic Laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT CAS). A ...
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