Number of found documents: 20
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Large Scale Motions in Turbulent Flows
Kellnerová, Radka; Jurčáková, Klára; Procházka, Pavel P.
2019 - English
Quadrant analysis based on the Reynolds decomposition was performed on the data from turbulent boundary layer flows above variously rough surfaces. An estimation of a convective velocity for events significant in terms of momentum flux, and the statistics of a length and amplitude of the individual events, together with their spectral analysis, was performed. Based on the analyses, we were able to detect a few individual sweep and ejection events with a length longer than 6δ, which could be considered as very large scale motions (VLSM). We also identified number of events with a longitudinal dimension equal to approximately 3δ labelled as large scale motions (LSM). The analyses were executed for various Reynolds numbers. The number of detected structures increases with the momentum of the flow. Keywords: wind tunnel; large scale motion; quadrant analysis Fulltext is available at external website.
Large Scale Motions in Turbulent Flows

Quadrant analysis based on the Reynolds decomposition was performed on the data from turbulent boundary layer flows above variously rough surfaces. An estimation of a convective velocity for events ...

Kellnerová, Radka; Jurčáková, Klára; Procházka, Pavel P.
Ústav termomechaniky, 2019

Assessing Quality of Boundary Layer Flows With the Diagnostic Plot
Jurčáková, Klára; Procházka, Pavel P.; Kellnerová, Radka
2019 - English
We experimentally investigated turbulent boundary layers over 4 rough surfaces and 1 smooth surface by particle image velocimetry for a range a free stream velocities. The obtained mean velocity vertical profiles were universally scaled by roughness length z₀ and friction velocity u*, but both parameters have to be obtained from the fit of the logarithmic or composite velocity pro le to the experimental data. Diagnostic plot, which relates turbulence intensity with the mean velocity showed good collapse of different free stream velocities for each surface. It became fully universal in its modified version when the roughness function was taken into an account. We found that turbulence intensities over our surfaces are higher than any published one and that they dependent on roughness length z₀*. Keywords: wind tunnel; turbulence intensity; rough-wall; friction velocity Fulltext is available at external website.
Assessing Quality of Boundary Layer Flows With the Diagnostic Plot

We experimentally investigated turbulent boundary layers over 4 rough surfaces and 1 smooth surface by particle image velocimetry for a range a free stream velocities. The obtained mean velocity ...

Jurčáková, Klára; Procházka, Pavel P.; Kellnerová, Radka
Ústav termomechaniky, 2019

Structure of the Wake Behind an Airfoil
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2019 - English
The wake behind an inclined plate simulating airfoil is to be studied experimentally. The vortical structures are identified eventually. Theirs topology and dynamical behaviour is to be studied in details using the Proper Orthogonal Decomposition method. The stereo time resolved Particle Image Velocimetry technique is used for the experimental research. The vortex trains with oblique orientation and chequered topology have been detected. Keywords: airfoil; boundary layer; wake; instability Fulltext is available at external website.
Structure of the Wake Behind an Airfoil

The wake behind an inclined plate simulating airfoil is to be studied experimentally. The vortical structures are identified eventually. Theirs topology and dynamical behaviour is to be studied in ...

Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
Ústav termomechaniky, 2019

Numerical simulation of flow in superpak family packings
Smutek, J.; Isoz, Martin
2018 - English
The distillation is currently the most energy-intensive technology of the chemical industry. Commonly, the distillation is performed in the columns lled with a structured packing. Structured packings are complex structures used to increase the size of the interface available for the mass transfer. Because of the high complexity of both the packings and the physical phenomena occurring during the distillation, the design of the distillation columns is still based mostly on empirical data. In this work, we concentrate on modeling the gas ow in the SuperPak family of structured packings. First, we propose an algorithm for automatic generation\nof the packing geometry. Next, we construct and validate a three-dimensional computational uid dynamics (CFD) model of gas ow through SuperPak 250.Y and SuperPak 350.Y packings. The model validation is done by comparing experimental data of dry pressure losses to the values computed by our model. The obtained di erence between the CFD estimates and experiments is bellow 10 %. Finally, we present a parametric study of the SuperPak 250.Y packing geometry. The devised modeling approach may be easily automated and used for optimization of the SuperPak type packing geometry with respect to the gas ow. Furthermore,\nthe proposed CFD model may be extended to account for the multiphase ow. Keywords: CFD; OpenFOAM; structured packing; distillation; absorption Fulltext is available at external website.
Numerical simulation of flow in superpak family packings

The distillation is currently the most energy-intensive technology of the chemical industry. Commonly, the distillation is performed in the columns lled with a structured packing. Structured packings ...

Smutek, J.; Isoz, Martin
Ústav termomechaniky, 2018

Model order reduction technique for large scale flow computations
Isoz, Martin
2018 - English
Current progress in numerical methods and available computational power combined with industrial needs promote the development of more and more complex models. However, such models are, due to their complexity, expensive from the point of view of the data storage and the time necessary for their evaluation. The model order reduction (MOR) seeks to reduce the computational complexity of large scale models. We present an application of MOR to the problems originating in the finite volume (FV) discretization of incompressible Navier-Stokes equations. Our approach to MOR is based on the proper orthogonal decomposition (POD)\nwith Galerkin projection. Moreover, the problems arising from the nonlinearities present in the original model are adressed within the framework of the discrete empirical interpolation method (DEIM). We provide a link between the POD-DEIM based MOR and OpenFOAM, which is an open-source CFD toolbox capable of solving even industrial scale problems. The availability of a link between OpenFOAM and POD-DEIM based MOR enables a direct order reduction for large scale systems originating in the industrial practice. Keywords: proper orthogonal decomposition; discrete empirical interpolation method; computational fluid dynamics; OpenFOAM Fulltext is available at external website.
Model order reduction technique for large scale flow computations

Current progress in numerical methods and available computational power combined with industrial needs promote the development of more and more complex models. However, such models are, due to their ...

Isoz, Martin
Ústav termomechaniky, 2018

Comparison of Finite Volume and Spectral/HP Methods on Navier - Stokes Equations for Unsteady Incompressible Flow
Pech, Jan; Louda, Petr
2018 - English
We provide a comparison of solutions to the incompressible Navier-Stokes equations obtained using codes based on finite volume and spectral element methods. Convergence properties are compared on test case with analytical solution. The dependence of Strouhal and Reynolds numbers for flow over a cylinder is reconstructed for both methods.\n\n Keywords: finite volume method; spectral element method; incompressible Navier-Stokes Fulltext is available at external website.
Comparison of Finite Volume and Spectral/HP Methods on Navier - Stokes Equations for Unsteady Incompressible Flow

We provide a comparison of solutions to the incompressible Navier-Stokes equations obtained using codes based on finite volume and spectral element methods. Convergence properties are compared on test ...

Pech, Jan; Louda, Petr
Ústav termomechaniky, 2018

Flow in Branched Channel
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2018 - English
Flow in a branched channel is investigated experimentally using the PIV method. The branches are issuing from the main cannel perpendicularly, all channels are of rectangular cross-section. The time-mean flow-fields in the main channel and in the branches are studied in details. Keywords: channel; branches; PIV Fulltext is available at external website.
Flow in Branched Channel

Flow in a branched channel is investigated experimentally using the PIV method. The branches are issuing from the main cannel perpendicularly, all channels are of rectangular cross-section. The ...

Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
Ústav termomechaniky, 2018

Low Cost Laser Rangefinder Evaluation
Krejsa, Jiří; Věchet, Stanislav
2018 - English
Laser rangefinders are essential tools in indoor mobile robot navigation. Lately several low-cost models become available, enabling the use of this type of sensor in broader range of applications. This paper evaluates the properties of currently (2018) the cheapest sensor available, particularly RPLidar A1M8, in order to determine whether it is usable in mobile robot development. As the sensor is based on triangulation principle, the increase of errors with the measured distance was expected, the experiments proved these expectations. Furthermore, the increasing, but linear trend in absolute measurement error was observed. The influence of surface material and color was also evaluated. The measurements indicate that RPLidar A1M8 can serve as a useful alternative for more expensive types of laser rangefinders. Keywords: laser rangefinder; mobile robot; localization Fulltext is available at external website.
Low Cost Laser Rangefinder Evaluation

Laser rangefinders are essential tools in indoor mobile robot navigation. Lately several low-cost models become available, enabling the use of this type of sensor in broader range of applications. ...

Krejsa, Jiří; Věchet, Stanislav
Ústav termomechaniky, 2018

DEM-CFD study of flow in a random packed bed
Šourek, M.; Isoz, Martin
2018 - English
Most catalytic surface reactions as well as other industrial applications take advantage of fixed packed bed reactors. Designers of these reactors rely mostly on empirical formulas derived for various simplifying assumptions, e.g. uniformly distributed porosity. The made simplifications and especially the assumption of uniformly distributed porosity fail if the tube to particle diameter ratio goes under 10 and the „wall effect“ becomes more significant. In such a case, the complete three-dimensional structure of the packed bed has to be considered. Thanks to ongoing improvements in numerical mathematics and computational power, the methods of computational fluid dynamics (CFD) have become a great tool for comprehensive description of the packed beds with low tube to particle diameter ratio. Three-dimensional simulations of the flow through two fixed beds differing in the type of the used particle are presented and compared with available experimental and empirical results. To generate the random fixed beds, we propose a custom approach based on the discrete element method (DEM) code implemented in open-source software Blender. Thereafter, OpenFOAM tools (snappyHexMesh, simpleFoam) are used for creation of the computational mesh and solution of the governing equations describing a single-phase flow in the packed bed. Keywords: CFD; DEM; random fixed bed; pressure drop; OpenFOAM Fulltext is available at external website.
DEM-CFD study of flow in a random packed bed

Most catalytic surface reactions as well as other industrial applications take advantage of fixed packed bed reactors. Designers of these reactors rely mostly on empirical formulas derived for various ...

Šourek, M.; Isoz, Martin
Ústav termomechaniky, 2018

Impact of Turbulence Generators on Turbulent Characteristics and Structures
Kellnerová, Radka; Jurčáková, Klára; Jaňour, Zbyněk
2017 - English
The turbulent generators are routinely used to produce very turbulent flows. Special type of vertically slenderize spires are applied to enhance turbulent diffusion from the surface upwards in order to increase the boundary layer depth. This paper studies the influence of variable upstream distance of generators on formation of both vortical and non-vortical organized structures within a test section. The 2-component 2-dimensional time-resolved particle image velocimetry measurement of the flow was performed in the wind channel with very rough surface. Intermittent flow dynamics was evaluated by means of higher order moments, vorticity, quadrant and wavelet analysis. The downstream evolution of the flow suggests that equilibrium between roughness- and spires-produced turbulence was reached at the distance of 7 spires height.\n Keywords: turbulence generator; wind channel; vorticity; quadrant analysis Fulltext is available at external website.
Impact of Turbulence Generators on Turbulent Characteristics and Structures

The turbulent generators are routinely used to produce very turbulent flows. Special type of vertically slenderize spires are applied to enhance turbulent diffusion from the surface upwards in order ...

Kellnerová, Radka; Jurčáková, Klára; Jaňour, Zbyněk
Ústav termomechaniky, 2017

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