Number of found documents: 2955
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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

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

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

Preliminary identification of damping properties of tonewood
Povolný, J.; Kozánek, Jan; Zapoměl, Jaroslav
2019 - English
Besides elasticity parameters, damping of the material is the crucial parameter of the function of a violin and also of other stringed instruments with a wooden soundboard. Assuming tonewood as an orthotropic linear elastic continuum, our aim is to contribute to hypothesis, that each orthotropic elastic constant has its appropriate loss factor - partial dampings. Dynamic experiments are based on the impulse excitation and the steady state harmonic response is calculated by Fourier transform of time-sampled measured signals (excitation and response). Frequency transfer function fitting identification method can determine complex modal and spectral eigen-parameters, mainly eigenfrequencies and eigendampings. Keywords: vibrating thin plate; modal analysis; identification of eigenfrequencies and eigendampings; damping; violin Available at various institutes of the ASCR
Preliminary identification of damping properties of tonewood

Besides elasticity parameters, damping of the material is the crucial parameter of the function of a violin and also of other stringed instruments with a wooden soundboard. Assuming tonewood as an ...

Povolný, J.; Kozánek, Jan; Zapoměl, Jaroslav
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

Reducing vibration amplitude by means of damping control in support elements of flexible rotors
Zapoměl, Jaroslav; Pešek, Luděk; Viet, La Duc; Savin, L.; Kozánek, Jan
2019 - English
Damping in the supports of rotors loaded by unbalance has influence on the vibration amplitude and critical speed of rotating machines. To minimize the oscillation amplitude during the rotor acceleration and running over the critical velocity, the damping in the support elements should be reduced. The reduction cannot be sudden but must be distributed in time. This requires to determine the proper moment of time when to start this manipulation and the time of its duration. This paper deals with investigation of the possibility of utilization of controllable squeeze film dampers lubricated by magnetorheological oil to accomplish this manipulation. Keywords: accelerating rotors; vibration reduction; magnetorheological dampers; damping control Available at various institutes of the ASCR
Reducing vibration amplitude by means of damping control in support elements of flexible rotors

Damping in the supports of rotors loaded by unbalance has influence on the vibration amplitude and critical speed of rotating machines. To minimize the oscillation amplitude during the rotor ...

Zapoměl, Jaroslav; Pešek, Luděk; Viet, La Duc; Savin, L.; Kozánek, Jan
Ústav termomechaniky, 2019

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