Number of found documents: 23
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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

Finite element modelling of elastic wave propagation in heterogeneous media
Kolman, Radek; Cho, S.S.; González, J. A.; Park, K.C.
2019 - English
In this contribution, we present an explicit scheme based on local time stepping respecting local wave speed and local stability limit for each finite element. The work aim is to suppress the spurious oscillations in wave propagation tasks in heterogeneous bars. Keywords: finite element modelling; elastic wave; heterogeneous media Fulltext is available at external website.
Finite element modelling of elastic wave propagation in heterogeneous media

In this contribution, we present an explicit scheme based on local time stepping respecting local wave speed and local stability limit for each finite element. The work aim is to suppress the spurious ...

Kolman, Radek; Cho, S.S.; González, J. A.; Park, K.C.
Ústav termomechaniky, 2019

The measurement of the heterogeneous particles in the steam
Bartoš, Ondřej; Hrubý, Jan; Ždímal, Vladimír; Kolovratník, Michal; Jiříček, I.; Moravec, Pavel; Zíková, Naděžda
2019 - English
The aim of this extended abstract is to reveal the work done as cooperation between several institutions which was presented and published in recent years (Kolovratník, 2014). The formation of droplets in low-pressure steam turbines has a significant impact on the efficiency of energy conversion due to the strongly nonequilibrium nature of this process . The condensed water also erodes the turbine blades. A very important question is to what extent heterogeneous nucleation contributes to the phase transition process . In the case of heterogeneous nucleation , the number of droplets depends only on the number of h eterogeneous particles in the system, whereas in the case of homogeneous nucleation, the number of created droplets is determined rather by the expansion rate - in a faster expansion, greater supersaturation and more droplets are formed until the released condensation enthalpy quenches the nucleation.\nThe specific number of droplets (number of droplets per unit mass of steam) formed in the turbine can be determined by optical probes, developed first by Walters and later in the Czech Republic improved by Petr and Kolovratník. Until recently, no information was available on the relative importance of heterogeneous nucleation in forming these droplets. Keywords: heterogeneous nucleation; steam turbine; ultrafine aerosol particles Fulltext is available at external website.
The measurement of the heterogeneous particles in the steam

The aim of this extended abstract is to reveal the work done as cooperation between several institutions which was presented and published in recent years (Kolovratník, 2014). The formation of ...

Bartoš, Ondřej; Hrubý, Jan; Ždímal, Vladimír; Kolovratník, Michal; Jiříček, I.; Moravec, Pavel; Zíková, Naděžda
Ústav termomechaniky, 2019

Anisotropy of Turbulent Flow around an Airfoil
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2019 - English
The flow around an airfoil is analyzed from the point of view turbulence anisotropy assessment. The turbulent flow-field in the vicinity of an airfoil is populated by vortices, in some locations they tend to regularity in orientation, i.e. to anisotropy. However in the wake behind the plate as well as in the core of the boundary layer on the plate suction side the turbulence is close to isotropic state. Keywords: airfoil; flow dynamics; turbulence; anisotropy Fulltext is available at external website.
Anisotropy of Turbulent Flow around an Airfoil

The flow around an airfoil is analyzed from the point of view turbulence anisotropy assessment. The turbulent flow-field in the vicinity of an airfoil is populated by vortices, in some locations they ...

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

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