Number of found documents: 2861
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Design of low-subsonic blade cascade model for aero-structural dynamic testing
Pešek, Luděk; Hála, Jindřich; Šulc, Petr; Chládek, Štěpán; Bula, Vítězslav; Uruba, Václav; Cibulka, Jan
2017 - English
Low-subsonic blade cascade model for aerodynamic testing was design in the Institute. The aim is to study the flow dynamics and flutter phenomenon in the cascade with moving blade profiles. The numerical calculations of two proposed cascades were performed for analysis of influence of stagger angle, incident angle of flow and inter-blade phase angles of the relative movement of blades. The results of numerical simulations of fluid dynamics of non-stationary flow both as viscid and non-viscid are presented. Futhermore the solution of the physical model of the designed cascade including excitation of profiles, measuring of the profile displacement and aerodynamic forces are described. Keywords: blade cascade; flutter; low-subsonic; experimental research Available at various institutes of the ASCR
Design of low-subsonic blade cascade model for aero-structural dynamic testing

Low-subsonic blade cascade model for aerodynamic testing was design in the Institute. The aim is to study the flow dynamics and flutter phenomenon in the cascade with moving blade profiles. The ...

Pešek, Luděk; Hála, Jindřich; Šulc, Petr; Chládek, Štěpán; Bula, Vítězslav; Uruba, Václav; Cibulka, Jan
Ústav termomechaniky, 2017

Transition Modelling on Separated Flow in Turbine Cascade
Louda, Petr; Příhoda, Jaromír; Kozel, K.
2017 - English
The work deals with numerical simulation of turbulent ow through turbine cascade by RANS model with model of transition to turbulence. Performance of two transition models is compared. First one is gamma-zeta model based on transition criteria, second one algebraic transition model based on the concept of laminar uctuations energy (Kubacki, Dick 2016). The criterion for transition in separated state is re-formulated in order to remove stream-wise non-local formulation. The performance of the transition models is observed on the shock wave - boundary layer interaction on turbine blade. Keywords: turbine cascade; transition model; separation bubble; shock wave-boundary layer interaction Fulltext is available at external website.
Transition Modelling on Separated Flow in Turbine Cascade

The work deals with numerical simulation of turbulent ow through turbine cascade by RANS model with model of transition to turbulence. Performance of two transition models is compared. First one is ...

Louda, Petr; Příhoda, Jaromír; Kozel, K.
Ústav termomechaniky, 2017

Modelling of running waves in turbine blades cascade
Půst, Ladislav; Pešek, Luděk
2017 - English
Dynamic properties of blades in the blade cascade excited by steam flow from the stationary bladed disk are investigated with the aim to explain origin and behaviour of running waves. It is shown that one of the most important reasons for existence of running waves is the running periodic forces from steam wakes due to different numbers of blades of stationary and rotating wheels. On a simplified computational model of disk with closed 10-blades bundle are presented resulting velocities, theirs directions and modes of forced running waves. The effect of these forced running waves on the existence of flutter waves will be shortly mentioned as well. Keywords: blade cascade; turbine disk; delay of excitation forces; forward; backward running waves Available at various institutes of the ASCR
Modelling of running waves in turbine blades cascade

Dynamic properties of blades in the blade cascade excited by steam flow from the stationary bladed disk are investigated with the aim to explain origin and behaviour of running waves. It is shown that ...

Půst, Ladislav; Pešek, Luděk
Ústav termomechaniky, 2017

Reduction of the energy losses by application of controllable squeeze film dampers
Zapoměl, Jaroslav; Ferfecki, Petr; Kozánek, Jan
2017 - English
The unbalance induces lateral oscillations of rotors and forces transmitted to the rotor casing. The squeeze film dampers with integrated rolling element bearings represent a technological solution, which enables to reduce their magnitude, and consequently the resistance against the rotor rotation. To achieve optimum performance of the damping devices, their damping effect must be adapable to the current rotor speed. This paper reports a proposal of a controllable squeeze film damper, the damping effect of which is controlled mechanically by shifting its outer ring in the axial direction. The developed mathematical model of the damper is based on assumptions of the classical theory of lubrication and is completed with implementation of a gas cavitation. The results of the computational simulations show that an appropriate control of the damping force enables to reduce the energy losses in a wide range of operating speeds. Keywords: squeeze film damper; controllable damping; friction in bearings; energy losses reduction Available at various institutes of the ASCR
Reduction of the energy losses by application of controllable squeeze film dampers

The unbalance induces lateral oscillations of rotors and forces transmitted to the rotor casing. The squeeze film dampers with integrated rolling element bearings represent a technological solution, ...

Zapoměl, Jaroslav; Ferfecki, Petr; Kozánek, Jan
Ústav termomechaniky, 2017

A short wave limit of the frequency equation for plane-stress nonaxisymmetric disc motions
Červ, Jan; Valeš, František; Adámek, V.
2017 - Czech
It is proved that the general frequency equation for plane-stress nonaxisymmetric disc motions tends for the first mode of propagation and for wavelengths very short when compared with the disc radius to the secular equation for Rayleigh waves. Keywords: frequency equation; elastic disc; Rayleigh waves Available at various institutes of the ASCR
A short wave limit of the frequency equation for plane-stress nonaxisymmetric disc motions

It is proved that the general frequency equation for plane-stress nonaxisymmetric disc motions tends for the first mode of propagation and for wavelengths very short when compared with the disc radius ...

Červ, Jan; Valeš, František; Adámek, V.
Ústav termomechaniky, 2017

Experimental modelling of phonation using artificial models of human vocal folds and vocal tracts
Horáček, Jaromír; Radolf, Vojtěch; Bula, Vítězslav; Košina, Jan
2017 - English
The study provides information on experimental research on a complete 1:1 scaled model of human phonation. The model includes human lungs, the trachea, the laryngeal part with artificial vocal folds and the vocal tracts designed for different vowels. The measurement set up enables modelling the time signals not easily measured in humans during phonation as for example fluctuations of the subglottic, laryngeal and oral pressures measured simultaneously with the glottis opening and the glottis area registered by a high-speed camera. The simulation of phonation is performed in the ranges of the airflow rate and the subglottic pressure typical for a normal humans' physiology. Keywords: biomechanics of voice Available at various institutes of the ASCR
Experimental modelling of phonation using artificial models of human vocal folds and vocal tracts

The study provides information on experimental research on a complete 1:1 scaled model of human phonation. The model includes human lungs, the trachea, the laryngeal part with artificial vocal folds ...

Horáček, Jaromír; Radolf, Vojtěch; Bula, Vítězslav; Košina, Jan
Ústav termomechaniky, 2017

Effect of turbulence in FE model of human vocal folds self-oscillation
Hájek, P.; Švancara, Pavel; Horáček, Jaromír; Švec, J.G.
2017 - English
The purpose of the study is to determine whether a turbulence model in fluid flow calculation affects the vocal folds (VF) vibration and the acoustics of human vocal tract (VT). The objective is examined using a two-dimensional (2D) finite element (FE) model of the fluid-structure-acoustic interaction for self-sustained oscillations of the VF. The FE model consists of the models of the VF, the trachea and a simplified model of the human VT. The developed FE model includes large deformations of the VF tissue and VF contact interrupting the airflow during glottis closure. The airflow is modelled by the unsteady viscous compressible Navier-Stokes equations, without and with the Shear Stress Transport (SST) turbulence model. Fluid-structure interaction (FSI) and morphing of the fluid mesh are realized using Arbitrary Lagrangian-Eulerian (ALE) approach. The method is applied on the FE model of the VT shaped for the Czech vowel [a:]. Also effect of varying stiffness of the superficial lamina propria (SLP) is analyzed. The numerical simulations showed that considering of the turbulence affects mainly higher frequencies apparent in a frequency spectrum of the VT acoustics. Keywords: simulation of phonation; SST turbulence model; fluid-structure-acoustic interaction; finite element method Available at various institutes of the ASCR
Effect of turbulence in FE model of human vocal folds self-oscillation

The purpose of the study is to determine whether a turbulence model in fluid flow calculation affects the vocal folds (VF) vibration and the acoustics of human vocal tract (VT). The objective is ...

Hájek, P.; Švancara, Pavel; Horáček, Jaromír; Švec, J.G.
Ústav termomechaniky, 2017

An explicit time scheme with local time stepping for one-dimensional wave propagation in a bimaterial bar
Kolman, Radek; Cho, S.S.; Gonzalez, J.G.; Park, K.C.; Berezovski, A.
2017 - English
In this paper, we test a two-time step explicit scheme with local time stepping. The standard explicit time scheme in finite element analysis is not able to keep accuracy of stress distribution through meshes with different local Courant numbers for each finite element. The used two-time step scheme with the diagonal mass matrix is based on the modification of the central difference method with pullback interpolation. We present a numerical example of one-dimensional wave propagation in a bimaterial elastic bar. Based on numerical tests, the employed time scheme with pullback interpolation and local stepping technique is able to eliminate spurious oscillations in stress distribution in numerical modelling of shock wave propagation in heterogeneous materials. Keywords: wave propagation in heterogeneous materials; explicit time integration; finite element method; local stepping; spurious oscillations Available at various institutes of the ASCR
An explicit time scheme with local time stepping for one-dimensional wave propagation in a bimaterial bar

In this paper, we test a two-time step explicit scheme with local time stepping. The standard explicit time scheme in finite element analysis is not able to keep accuracy of stress distribution ...

Kolman, Radek; Cho, S.S.; Gonzalez, J.G.; Park, K.C.; Berezovski, A.
Ústav termomechaniky, 2017

Investigation of droplet nucleation in CCS relevant systems – design and testing of the expansion chamber
Čenský, Miroslav; Hrubý, Jan; Vinš, Václav; Hykl, Jiří; Šmíd, Bohuslav
2017 - English
A unique in-house designed experimental apparatus for investigation of nucleation of droplets in CCS relevant systems is being developed by the present team. The apparatus allows simulating various processes relevant to CCS technologies. Gaseous mixtures with CO2 are prepared in a Mixture Preparation\nDevice (MPD) based on accurate adjustment of flow rates of individual components [EPJ Web of Conferences 143, 02140 (2017)]. The mixture then flows into an expansion chamber, where it undergoes a rapid adiabatic expansion. As a consequence of adiabatic cooling, the mixture becomes supersaturated and nucleation and simultaneous growth of droplets occurs. In this study, we describe the design and testing of the expansion part of the experimental setup. The rapid expansion was realized using two valve systems, one for low pressures (up to 0.7 MPa) and the other for high pressures (up to 10 MPa). A challenge for a proper design of the expansion system is avoiding acoustic oscillations. These can occur either in the mode of Helmholtz resonator, where the compressible gas in the chamber acts as a spring and the rapidly moving\ngas in the valve system as a mass, or in the “flute” mode, where acoustic waves are generated in a long outlet tubing.\n Keywords: carbon capture and storage; expansion chamber; experiment Available at various institutes of the ASCR
Investigation of droplet nucleation in CCS relevant systems – design and testing of the expansion chamber

A unique in-house designed experimental apparatus for investigation of nucleation of droplets in CCS relevant systems is being developed by the present team. The apparatus allows simulating various ...

Čenský, Miroslav; Hrubý, Jan; Vinš, Václav; Hykl, Jiří; Šmíd, Bohuslav
Ústav termomechaniky, 2017

Physical modelling axisymmetric diffusors by plane models
Uruba, Václav
2017 - English
Diffusers with axisymmetric geometry are used very often in technical applications, they are characterized by circular cross-section along the flow axis. Such geometry is not suitable for application of optical methods, so the plane model with rectangular cross-section is used instead very often. However the flow inside such model could be significantly different as for velocity and pressure fields. The physical similarity of 1D flow in axisymmetric diffusers and plane models will be studied in details. The plane model opening angle is suggested to optimize velocity and pressure distributions in the model. Keywords: diffusor; pressure gradient; axisymmetric geometry; plane model Available at various institutes of the ASCR
Physical modelling axisymmetric diffusors by plane models

Diffusers with axisymmetric geometry are used very often in technical applications, they are characterized by circular cross-section along the flow axis. Such geometry is not suitable for application ...

Uruba, Václav
Ústav termomechaniky, 2017

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