Number of found documents: 2503
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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

Application of non-contact vibration measurements on a 48“ blade under low load condition
Kubín, Z.; Liška, J.; Míšek, T.; Procházka, Pavel
2017 - English
The paper describes in detail a Tip-Timing measurement on a combined cycle power plant with a steam turbine power output of 270MW. Newly developed magnetoresistive and optical sensors were used as well as standard eddy-current sensors to measure blade vibration under low load condition and variable back pressure. New hardware solution for the Tip-Timing measurement will is presented as well as results of measurements of relative amplitudes and excited nodal diameters. Keywords: steam turbine; non-contact vibration measurement; magnetoresistive sensor; optical sensor Available at various institutes of the ASCR
Application of non-contact vibration measurements on a 48“ blade under low load condition

The paper describes in detail a Tip-Timing measurement on a combined cycle power plant with a steam turbine power output of 270MW. Newly developed magnetoresistive and optical sensors were used as ...

Kubín, Z.; Liška, J.; Míšek, T.; Procházka, Pavel
Ústav termomechaniky, 2017

Some experimentally determined properties of a profile in case of self-excited oscillations in subsonic flow
Vlček, Václav; Zolotarev, Igor; Kozánek, Jan; Šidlof, Petr; Štěpán, M.
2017 - English
In the wind tunnel of the Institute of Thermomechanics of the AS CR,v .v. i., experiments were realized with the profile NACA0015 in the presence of the self-excited oscillation. The oscillation of the profile with pitch and plunge degrees of freedom was excited by the subsonic air flow. The plunge support had the same elasticity for all experiments, the pitch support had seven different values of elasticity. Within experiments different types of self-excited vibration (flutter, stall flutter, deep stall flutter) were realized. Range of Mach numbers were M=0.08–0.45, when the chord length is used as the characteristic dimension of the profile. The frequency and amplitude characteristics of the oscillating profile were experimentally determined.\n Keywords: airfoil; aeroelasciticy; dynamic stall; stall flutter; limit cycle oscillations; self -excited vibrations Available at various institutes of the ASCR
Some experimentally determined properties of a profile in case of self-excited oscillations in subsonic flow

In the wind tunnel of the Institute of Thermomechanics of the AS CR,v .v. i., experiments were realized with the profile NACA0015 in the presence of the self-excited oscillation. The oscillation of ...

Vlček, Václav; Zolotarev, Igor; Kozánek, Jan; Šidlof, Petr; Štěpán, M.
Ústav termomechaniky, 2017

Aspects of energy storage systems focusing on flywheel technologies
Zapoměl, Jaroslav; Kozánek, Jan
2017 - English
The energy storage devices are used to reduce variation of the power transmitted in complex technological systems. The individual technologies are based on different physical principles and are applicable in different industrial fields. This paper focuses on aspects of the flywheel storage devices that have a direct impact on their design, technological parametres, and extent of their application. Keywords: energy storage systems; flywheel technology; ultra-low friction bearings Available at various institutes of the ASCR
Aspects of energy storage systems focusing on flywheel technologies

The energy storage devices are used to reduce variation of the power transmitted in complex technological systems. The individual technologies are based on different physical principles and are ...

Zapoměl, Jaroslav; Kozánek, Jan
Ústav termomechaniky, 2017

Proposal of hyperelastic proportional damping as dissipated energy model of hard rubbers
Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Košina, Jan; Cibulka, Jan
2017 - English
The paper deals with a stress analysis of hard rubber under large torsion deformations. This study was motivated by effort to find the dependency the dissipated energy on the deformation energy. Based on the results of an experiment, a function of dissipation energy of hard rubbers for finite strains using the theory hyperelasticity was proposed herein analogically as a proportional damping for elastic theory. Samples of hard rubber of different hardness (EPDM, Silicone) were dynamically tested on the developed torsional test-rig at different frequencies, amplitudes. First the Mooney Rivlin model (MRM) for a shear case of loading was analytically developed and then MRM constants were attained by fitting of the MRM to the experimental torsion-deformation curve. These constants were used to obtain the deformation energy of the MRM models. The coefficients of hyperelastic proportional damping relating a dissipated energy to a strain energy were evaluated for tested rubbers on the basis of experimental results. Keywords: torsion vibration; large deformation; hyperelasticity; dissipated energy; deformation energy Available at various institutes of the ASCR
Proposal of hyperelastic proportional damping as dissipated energy model of hard rubbers

The paper deals with a stress analysis of hard rubber under large torsion deformations. This study was motivated by effort to find the dependency the dissipated energy on the deformation energy. Based ...

Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Košina, Jan; Cibulka, Jan
Ústav termomechaniky, 2017

On Finite Element Approximation of Flow Induced Vibration of Elastic Structure
Valášek, J.; Sváček, P.; Horáček, Jaromír
2017 - English
In this paper the fluid-structure interaction problem is studied on a simplified model of the human vocal fold. The problem is mathematically described and the arbitrary Lagrangian-Eulerian method is applied in order to treat the time dependent computational domain. The viscous incompressible fluid flow and linear elasticity models are considered. The fluid flow and the motion of elastic body is approximated with the aid of fininite element method. An attention is paid to the applied stabilization technique. The whole algorithm is implemented in an in-house developed solver. Numerical results are presented and the influence of different inlet boundary conditions is discused. Keywords: stabilized finite element method; 2D Navier-Stokes equations; vocal folds; aeroelasticity Available at various institutes of the ASCR
On Finite Element Approximation of Flow Induced Vibration of Elastic Structure

In this paper the fluid-structure interaction problem is studied on a simplified model of the human vocal fold. The problem is mathematically described and the arbitrary Lagrangian-Eulerian method is ...

Valášek, J.; Sváček, P.; Horáček, Jaromír
Ústav termomechaniky, 2017

Greep analysis of-piece of the steam distributor
Gabriel, Dušan; Masák, Jan; Plešek, Jiří
2017 - English
The finite element analysis of the steam distributor of the CHEMOPETROL heating plant T200 was analyzed under creep conditions. Material properties were described by the probabilistic exponential model with damage. The purpose of the analysis was to compare the original version and the proposed design modification applied to one of T-pieces of the distributor when the original contact algorithm was employed to simulate the interaction between the collar and the pipe. Keywords: creep analysis; T-piece of the steam distributor; FEM Available at various institutes of the ASCR
Greep analysis of-piece of the steam distributor

The finite element analysis of the steam distributor of the CHEMOPETROL heating plant T200 was analyzed under creep conditions. Material properties were described by the probabilistic exponential ...

Gabriel, Dušan; Masák, Jan; Plešek, Jiří
Ústav termomechaniky, 2017

Dissipated energy of hard rubbers at dynamic torsional finite straining
Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Cibulka, Jan; Košina, Jan
2017 - English
The paper deals with a stress analysis of hard rubber under large torsion deformations. This study was motivated by effort to find the dependency the dissipated energy on the deformation energy. Based on the results of an experiment, a function of dissipation energy of hard rubbers for finite strains using the theory hyperelasticity was proposed herein analogically as a prportional damping for elastic theory. Samples of hard rubber of different hardness (EPDM, Silcone) were dynamically tested on the developed torsional test-rig at different frequencies, amplitudes. First the Mooney Rivlin model (MRM) for a shear case of loading was analytically developed and then MRM constants were attained by fitting of the MRM to the experimental torsion-deformation curve. These constants were used to obtain the deformation energy of the MRM models. The coefficients of hyperelastic proportional damping relating a dissipated energy to a strain energy were evaluated for tested rubbers on the basis of experimental results. Keywords: hard rubber; torsion vibration; large deformation Available at various institutes of the ASCR
Dissipated energy of hard rubbers at dynamic torsional finite straining

The paper deals with a stress analysis of hard rubber under large torsion deformations. This study was motivated by effort to find the dependency the dissipated energy on the deformation energy. Based ...

Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Cibulka, Jan; Košina, Jan
Ústav termomechaniky, 2017

Možnosti zvyšování účinnosti indukčních motorů použitím kombinovaného statorového vinutí
Schreier, Luděk; Bendl, Jiří; Chomát, Miroslav
2017 - Czech
Jsou analyzovány dvě základní varianty zapojení kombinovaného statorového vinutí asynchronního stroje. Účelem použití kombinovaného vinutí je potlačení vybraných skupin vyšších prostorových harmonických proudové vrstvy a indukce ve vzduchové mezeře a toku ve jhu za účelem snížení ztrát a zlepšení účinnosti. Jsou uvedeny diferenciální rovnice pro obě uvažované varianty. Na základě numerického řešení těchto rovnic byla ukázána schopnost jednotlivých variant potlačovat vyšší harmonické. Platnost rovnic byla ověřena experimentálním měřením na fyzikálním modelu asynchronního stroje se statorovým kombinovaným vinutím. The paper analyses two basic variants of the combined connection of the stator winding of an induction machine. The aim of the use combined winding is to suppress the selected groups of higher spatial harmonics of the current layer and induction in the air gap and the flux in the yoke and thus lower the losses and improve the efficiency. There are given differential equations for both the variants.On the basis of a numerical solution of these equations, the ability of the two variants to suppress higher harmonics has been shown. The validity of the equations has been verified by experimental measurement on a physical model of an induction machine with the stator combined winding. Keywords: induction machine; efficiency; higher spatial harmonics Available at various institutes of the ASCR
Možnosti zvyšování účinnosti indukčních motorů použitím kombinovaného statorového vinutí

Jsou analyzovány dvě základní varianty zapojení kombinovaného statorového vinutí asynchronního stroje. Účelem použití kombinovaného vinutí je potlačení vybraných skupin vyšších prostorových ...

Schreier, Luděk; Bendl, Jiří; Chomát, Miroslav
Ústav termomechaniky, 2017

Surface tension of aqueous binary mixtures under the supercooled conditions – Development of the measuring technique and preliminary data for water + lower alcohols
Vinš, Václav; Hykl, Jiří; Nikl, Zbyněk; Čenský, Miroslav; Hrubý, Jan
2017 - English
An experimental apparatus originally developed for the measurement of surface tension of supercooled water was modified such that it allows for measurement of binary aqueous mixtures. The measuring principle based on the capillary rise technique is similar to that employed in the previous measurements with pure water [J. Hrubý et al., J. Phys. Chem. Lett. 5 (2014) 425 and V. Vinš et al., J. Phys. Chem. B 119 (2015) 5567]. The temperature dependence of the surface tension is determined from the\nmeasured height of the liquid column elevated in a vertical capillary tube with an inner diameter of 0.32 mm. The aqueous liquid rises to a height of 60 mm to 95 mm depending on the solute concentration and the temperature. Preliminary tests performed with the binary mixtures of water with methanol, ethanol, and n-propanol at various concentrations and temperatures down to –28 °C approved functionality of the measuring technique. Some difficulties, such as influence of impurities on the liquid column elevation or formation of bubbles in the liquid column, were observed. The experimental apparatus is further being modified in order to obtain more accurate data for various aqueous mixtures. Keywords: aqueous mixture; surface tension; supercooled liquid Available at various institutes of the ASCR
Surface tension of aqueous binary mixtures under the supercooled conditions – Development of the measuring technique and preliminary data for water + lower alcohols

An experimental apparatus originally developed for the measurement of surface tension of supercooled water was modified such that it allows for measurement of binary aqueous mixtures. The measuring ...

Vinš, Václav; Hykl, Jiří; Nikl, Zbyněk; Čenský, Miroslav; Hrubý, Jan
Ústav termomechaniky, 2017

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