Number of found documents: 2953
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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

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

Measurements on KR-D-2 Blade Cascade
Šimurda, David; Luxa, Martin; Radnic, Tomáš; Hála, Jindřich
2019 - English
This report contains results and evaluation of aerodynamic measurements conducted on second variant of transonic compressor blade cascade. Keywords: transonic compressor blade; aerodynamic measurements; axial compressor Available at various institutes of the ASCR
Measurements on KR-D-2 Blade Cascade

This report contains results and evaluation of aerodynamic measurements conducted on second variant of transonic compressor blade cascade.

Šimurda, David; Luxa, Martin; Radnic, Tomáš; Hála, Jindřich
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

Report on the reference densities of water and air employed for the adjustment of vibrating tube density meter
Vinš, Václav; Prokopová, Olga
2019 - English
Zpráva představuje souhrn několika modelů pro určení referenčních hustot čisté vody a vlhkého vzduchu při atmosférickém tlaku, které jsou potřebné k teplotní kalibraci hustoměru s vibrační trubicí Anton Paar DMA 5000 M. Při nastavení přístroje využívaného v Laboratoři termofyzikálních vlastností vzešla řada technických otázek ohledně kalibrace přístroje. Tato zpráva slouží zejména jako podklad k diskuzi se zástupci společnosti Anton Paar. S použitím softwaru pro technické výpočty Matlab byly vytvořeny programy pro výpočet hustoty vody pomocí stavové rovnice IAPWS-95 od Wagnera a Pruße (2002), CIPM standardu od Tanaky a kol. (2001) a vztahu od Spiewecka a Bettina (1992). Pro vlhký vzduch byl sestaven model na základě IAPWS Guideline G8-10 (2010) založeném na stavové rovnici pro suchý vzduch od Lemmona a kol. (2000) a stavové rovnici pro vodu IAPWS-95. Výsledky byly porovnány s CIPM standardem od Picarda a kol. (2008) a zjednodušeným vztahem od Spiewecka a Bettina (1992). V závěrečné části jsou prezentována data naměřená v Laboratoři termofyzikálních vlastností pro čistou vodu v teplotním rozsahu 2 až 50 °C pro různá nastavení referenčních vztahů pro hustoty vody a vlhkého vzduchu použité při kalibraci přístroje.\n Available at various institutes of the ASCR
Report on the reference densities of water and air employed for the adjustment of vibrating tube density meter

Zpráva představuje souhrn několika modelů pro určení referenčních hustot čisté vody a vlhkého vzduchu při atmosférickém tlaku, které jsou potřebné k teplotní kalibraci hustoměru s vibrační trubicí ...

Vinš, Václav; Prokopová, Olga
Ústav termomechaniky, 2019

Influence of tissue changes in superficial lamina propria on production of Czech vowels
Hájek, P.; Švancara, P.; Horáček, Jaromír; Švec, J.
2019 - English
Superficial lamina propria (SLP) is a water-like vocal fold (VF) layer located directly under overlying epithelium. Its material properties affect VF motion and thus resulting spectrum of produced sound. Influence of stiffness and damping of the SLP on sound spectrum of Czech vowels is examined using a two-dimensional (2D) finite element (FE) model of a human phonation system. The model consists of the VF (structure model) connected with an idealized trachea and vocal tract (VT) (fluid models). Five VTs for all Czech vowels [a:], [e:], [i:], [o:] and [u:] were used and their geometry were based on MRI data. Fluid flow in the trachea and VT was modelled by unsteady viscous compressible Navier-Stokes equations. Such a formulation enabled numerical simulation of a fluid-structure-acoustic interaction (FSAI). Self-sustained oscillations of the VF were described by a momentum equation including large deformations and a homogeneous linear elastic model of material was used. Fluid and structure solvers exchange displacements and boundary forces in each iteration. During closed phase VFs are in contact and fluid flow is separated. We can observe that both the damping and the stiffness of the SLP substantially influence the amplitude and frequency of VFs vibration as well as the open time of the glottis.\n Keywords: simulation of phonation; fluid-structure-acoustic interaction; czech vowels; finite element method; biomechanics of voice Available at various institutes of the ASCR
Influence of tissue changes in superficial lamina propria on production of Czech vowels

Superficial lamina propria (SLP) is a water-like vocal fold (VF) layer located directly under overlying epithelium. Its material properties affect VF motion and thus resulting spectrum of produced ...

Hájek, P.; Švancara, P.; Horáček, Jaromír; Švec, J.
Ústav termomechaniky, 2019

Experimental and computer modelling study of glottal closing velocity during phonation
Horáček, Jaromír; Radolf, Vojtěch; Bula, Vítězslav; Šidlof, P.; Geneid, A.; Laukkanen, A. M.
2019 - English
This preliminary study shows that the impact stress between the colliding vocal folds during phonation should not be evaluated from the maximum velocity of the glottal closing because the velocity of the closing diminishes just before the glottal closure. This phenomenon, which can be caused by a pressure cushion effect in the fast narrowing glottal gap, is demonstrated with measurements from high speed camera images recorded from human and on a physical laboratory model for vowel [u:] phonation and on a three-mass computer model employing a Hertz model of impact force. For a more detailed future study of this phenomenon a faster camera has to be used. \n Keywords: impact stress; maximum glottal area delination rate (MADR); High speed imaging Available at various institutes of the ASCR
Experimental and computer modelling study of glottal closing velocity during phonation

This preliminary study shows that the impact stress between the colliding vocal folds during phonation should not be evaluated from the maximum velocity of the glottal closing because the velocity of ...

Horáček, Jaromír; Radolf, Vojtěch; Bula, Vítězslav; Šidlof, P.; Geneid, A.; Laukkanen, A. M.
Ústav termomechaniky, 2019

Simulation of Supersonic Flow Through the Tip-Section Turbine Blade Cascade with a Flat Profile
Musil, Josef; Příhoda, Jaromír; Fürst, J.
2019 - English
The contribution presents results of the numerical simulation of 2D compressible flow through the tip-section turbine blade cascade with a flat profile and the supersonic inlet. The simulation was carried out by the OpenFOAM code using the Favre-averaged NavierStokes equations completed by the two-equation SST turbulence model and the γ-Reθ bypass transition model. Predictions carried out for nominal conditions were focused particularly on the relation between the inlet flow angle and the inlet Mach number. Further, the effect of the shock-wave/boundary layer interaction on the skin friction coefficient was investigated. Numerical results were compared with experimental data. Keywords: supersonic tip-section blade cascade; CFD; transition modelling Available at various institutes of the ASCR
Simulation of Supersonic Flow Through the Tip-Section Turbine Blade Cascade with a Flat Profile

The contribution presents results of the numerical simulation of 2D compressible flow through the tip-section turbine blade cascade with a flat profile and the supersonic inlet. The simulation was ...

Musil, Josef; Příhoda, Jaromír; Fürst, J.
Ústav termomechaniky, 2019

Aerodynamic transfer of energy to vibrating vocal folds for different driving mechanisms
Valášek, J.; Sváček, P.; Horáček, Jaromír
2018 - English
This paper studies the mutual energy transfer between the fluid flow, described by incompressible Navier-Stokes equations, and the elastic body represented by vocal folds. The aerodynamic energy transfer function describes the amount and more importantly the sign of the energy exchange. It determines if the vocal fold vibrations are self-excited or prescribed.The energy transfer function is studied for three different driving mechanisms introduced by different inlet boundary conditions (BC). The most frequently used inlet BCs for incompressible model of fluid flow approximated by the finite element method are either Dirichlet BC giving the inlet velocity or do-nothing type of BC prescribing the pressure difference between the inlet and the outlet. Since the numerical simulations with both aforementioned BCs do not provide results observed experimentally the newly introduced BC based on the penalization approach seems as remedy. The numerical model consists of strongly coupled partitioned scheme based on the stabilized finite element method.\n\n Keywords: inlet boundary conditions; weakly imposed Dirichlet boundary condition; energy transfer function; finite element method Available at various institutes of the ASCR
Aerodynamic transfer of energy to vibrating vocal folds for different driving mechanisms

This paper studies the mutual energy transfer between the fluid flow, described by incompressible Navier-Stokes equations, and the elastic body represented by vocal folds. The aerodynamic energy ...

Valášek, J.; Sváček, P.; Horáček, Jaromír
Ústav termomechaniky, 2018

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