Number of found documents: 2589
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On the 3D Dynamics of the Wake Behind a Circular Cylinder
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2020 - English
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. Keywords: circular cylinder; wake; 3D structure; POD Fulltext is available at external website.
On the 3D Dynamics of the Wake Behind a Circular Cylinder

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 ...

Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
Ústav termomechaniky, 2020

An experimental investigation of yield surfaces anisotropies
Štefan, Jan; Parma, Slavomír; Marek, René; Plešek, Jiří; Feigenbaum, H. P.; Ciocanel, C.
2020 - English
This contribution is dedicated to a rigorous experimental procedure for evaluation of yield surfaces of common metallic materials. This yield surface tracing procedure employs thin-walled tubular specimens to identify individual yield points of the material under arbitrary combinations of axial load and torque. A yield point is identified on the basis of a prescribed threshold for the effective plastic strain that is being continuously and fully automatically evaluated throughout the test. The experimental results generated with this tracing method are promising, leading to shapes of the yield surfaces conform with the von Mises criterion. The proposed methodology can effectively capture the YS shape. Keywords: experimental mechanics; yield surface; directional distortional hardening; metallic materials Available at various institutes of the ASCR
An experimental investigation of yield surfaces anisotropies

This contribution is dedicated to a rigorous experimental procedure for evaluation of yield surfaces of common metallic materials. This yield surface tracing procedure employs thin-walled tubular ...

Štefan, Jan; Parma, Slavomír; Marek, René; Plešek, Jiří; Feigenbaum, H. P.; Ciocanel, C.
Ústav termomechaniky, 2020

Modification of the Algebraic Transition Model for Wall Roughness Effect Including a Rough Strip
Straka, P.; Příhoda, Jaromír
2020 - English
The contribution deals with the simulation of the laminar/turbulent transition on a rough wall. The algebraic transition model taking into account wall roughness according to Straka and Příhoda [8] was further extended for the effect of short rough strip near the leading edge. The proposed correlation was tested by means of incompressible flow over a flat plate covered by sand paper and around the NACA 0012 airfoil with a rough strip near the leading edge. The agreement with experiments is appropriate nevertheless the applicability of the correlation is limited due to the lack of relevant experimental results. Keywords: bypass-transition; wall roughness; rough strip Fulltext is available at external website.
Modification of the Algebraic Transition Model for Wall Roughness Effect Including a Rough Strip

The contribution deals with the simulation of the laminar/turbulent transition on a rough wall. The algebraic transition model taking into account wall roughness according to Straka and Příhoda [8] ...

Straka, P.; Příhoda, Jaromír
Ústav termomechaniky, 2020

Study on Performance of Various Turbulent Heat Transfer Closures
Louda, Petr; Příhoda, Jaromír
2020 - English
The work compares results of several turbulent heat flux models with different complexity. Authors consider eddy diffusivity model as well as generalized gradient hypothesis and explicit algebraic closures. The results are obtained for backward facing step with heated bottom wall and compared with measurements. Keywords: backward facing step; turbulent heat flux Fulltext is available at external website.
Study on Performance of Various Turbulent Heat Transfer Closures

The work compares results of several turbulent heat flux models with different complexity. Authors consider eddy diffusivity model as well as generalized gradient hypothesis and explicit algebraic ...

Louda, Petr; Příhoda, Jaromír
Ústav termomechaniky, 2020

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

Vyšetřování proudění uvnitř přirozeně větraného kravína: předběžné výsledky z experimentů v aerodynamickém tunelu
Nosek, Štěpán; Kluková, Zuzana; Kellnerová, Radka; Jakubcová, Michala; Jaňour, Zbyněk
2019 - Czech
V této studii byly kvalitativně porovnány střední vektorové (složky podélné a vertikální rychlosti) a skalární pole (intenzita turbulence) v měřítkovém (1:50) modelu přirozeně větraného kravína. Tato kvalitativní srovnání jasně poukazují na účinek simulované mezní vrstvy atmosféry (MVA) a konfiguraci otvorů na proudové charakteristiky uvnitř kravína. MVA mírně drsného terénu vytváří vyšší rychlosti jak u vstupních a výstupních otvorů, tak uvnitř kravina, než MVA velmi drsného terénu. Intenzita turbulence je však více závislá na konfiguraci otvoru. Například, ačkoli MVA byla velmi drsná, a tedy turbulentnější, byly v případě středních otvorů pozorovány nižší intenzity turbulence než u středně drsné MVA. The mean vector (longitudinal and vertical velocity components) and scalar (turbulence intensity) fields within a scale (1:50) model of naturally ventilated cattle barn were qualitatively compared in this study. These qualitative comparisons clearly show the effect of the simulated atmospheric boundary layer (ABL) and the opening configuration on the flow characteristics within the barn. ABL of moderately rough terrain produces higher velocities at both the inlet and the outlet openings and inside the barn than that ABL of very rough terrain. However, the intensity of the turbulence is more dependent on the configuration of the opening. For instance, although ABL was very rough and therefore more turbulent, lower turbulence intensities were observed for that ABL than for the moderately rough ABL in the case of middle openings. Keywords: atmospheric boundary layer; livestock building; natural ventilation; wind-tunnel Available at various institutes of the ASCR
Vyšetřování proudění uvnitř přirozeně větraného kravína: předběžné výsledky z experimentů v aerodynamickém tunelu

V této studii byly kvalitativně porovnány střední vektorové (složky podélné a vertikální rychlosti) a skalární pole (intenzita turbulence) v měřítkovém (1:50) modelu přirozeně větraného kravína. Tato ...

Nosek, Štěpán; Kluková, Zuzana; Kellnerová, Radka; Jakubcová, Michala; Jaňour, Zbyněk
Ústav termomechaniky, 2019

Excitation of wheel blades by axial electromagnet at different regimes
Voronova, Evgeniya; Maturkanič, Dušan
2019 - English
The paper describes the natural frequency identification experiment and results of measuring of blade vibration characteristics excitate by one axial electromagnet at different regimes. The measurements were performed in the laboratory of the rotational laser vibrometry originated at the Institute of Thermomechanics AS CR, v.v.i. Keywords: vibration; blade; magnet; frequency Available at various institutes of the ASCR
Excitation of wheel blades by axial electromagnet at different regimes

The paper describes the natural frequency identification experiment and results of measuring of blade vibration characteristics excitate by one axial electromagnet at different regimes. The ...

Voronova, Evgeniya; Maturkanič, Dušan
Ústav termomechaniky, 2019

Experimentální vyšetřování vhodné poréznosti protiprašné stěny
Nosek, Štěpán
2019 - Czech
Článek seznamuje čtenáře se základními principy fyzikálního modelování atmosférické mezní vrstvy ve větrných tunelech a jejich aplikací na řešení prašnosti. Je uveden praktický příklad použití těchto metod v rámci řešení šíření prašnosti z pásových dopravníků do bezprostředního okolí protiprašnou stěnou. The paper introduces the reader to the basic principles of physical modelling of the atmospheric boundary layer in wind tunnels and their application to the solution of dustiness. A practical example elucidates the use of these methods in the solution of dustiness from conveying belts to immediate surroundings. Keywords: atmospheric boundary layer; physical modelling; porosity; dustiness; wind tunnel Available at various institutes of the ASCR
Experimentální vyšetřování vhodné poréznosti protiprašné stěny

Článek seznamuje čtenáře se základními principy fyzikálního modelování atmosférické mezní vrstvy ve větrných tunelech a jejich aplikací na řešení prašnosti. Je uveden praktický příklad použití těchto ...

Nosek, Štěpán
Ústav termomechaniky, 2019

Příčina mechanického chvění těžních synchronních motorů Palašer a jeho odstranění
Pavelka, J.; Šimek, J.; Kobrle, P.; Kokeš, Petr
2019 - Czech
Příspěvek popisuje postup a výsledek analýzy mechanického rozkmitávání těžních strojů na dole Palašer v Ruské federaci. Jako příčina byla určena změna velikosti magnetického toku ve vzduchové mezeře vlivem drážkování statorů. Provedené simulace prokázaly možnost odstranění změny magnetického toku injektáží vhodných napětí statorového vinutí. V dalším je popsána realizace této injektáže pomocí přímovazební kompenzace střídavé složky momentu. Na závěr jsou uvedeny oscilografické záznamy před a po injektáži. The paper describes the procedure and the result of analysis of mechanical vibrations of mining machines at the Palašer mine in the Russian Federation. The cause of these vibrations was the change in the magnitude of the magnetic flux in the air gap. The simulations showed the possibility of eliminating these changes in\nmagnetic flux by injecting suitable voltages into the stator windings. The implementation of this injection is further described by torque variable component feed-direct compensation. Finally, oscillography records are presented before and after injection. Keywords: mining machine; synchronous motor; indirect frequency converter; Maxwell force; resonant frequency; feed-direct compensation; injected voltage Available at various institutes of the ASCR
Příčina mechanického chvění těžních synchronních motorů Palašer a jeho odstranění

Příspěvek popisuje postup a výsledek analýzy mechanického rozkmitávání těžních strojů na dole Palašer v Ruské federaci. Jako příčina byla určena změna velikosti magnetického toku ve vzduchové mezeře ...

Pavelka, J.; Šimek, J.; Kobrle, P.; Kokeš, Petr
Ústav termomechaniky, 2019

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