Number of found documents: 2874
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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

Modelling of Flow in Linear Blade Cascade with Thick Trailing Edge at a Lower Reynolds Number
Straka, P.; Příhoda, Jaromír
2017 - English
In the paper there are compared results of numerical simulation of compressible turbulent flow through a low-pressure turbine blade cascade with relatively thick trailing edges for various physical models. Steady, unsteady, fully turbulent, transitional, two-dimensional and three-dimensional models are compared. Results show that: a) steady simulation gives an incorrect prediction of the boundary layer development, b) two-dimensional unsteady simulation leads to inaccurate prediction of the far wake development and c) only three-dimensional unsteady transitional simulation gives sufficiently accurate prediction. Results of numerical simulations are compared with the experimental data. Keywords: linear blade cascade; boundary layer transition; vortex series Available at various institutes of the ASCR
Modelling of Flow in Linear Blade Cascade with Thick Trailing Edge at a Lower Reynolds Number

In the paper there are compared results of numerical simulation of compressible turbulent flow through a low-pressure turbine blade cascade with relatively thick trailing edges for various physical ...

Straka, P.; Příhoda, Jaromír
Ústav termomechaniky, 2017

Posouzení výpočtové dokumentace návrhu opravy heterogenního svárového spoje nátrubku PG technologií Weld Overlay. Dokumentace k výpočtovému modelu MKP pro hodnocení kritické velikosti trhliny.
Pták, Svatopluk; Masák, Jan; Gabriel, Dušan
2017 - Czech
V první cásti zprávy je vypracováno posouzení výpoctové dokumentace návrhu opravy heterogenního svarového spoje nátrubku superhavarijního napájení parogenerátoru v JE Dukovany technologií Weld Overlay (WOL). V druhé cásti zprávy je shrnuta dokumentace k vytvorenému MKP modelu nátrubku s trhlinou, který bude použit k výpoctu kritické velikosti trhliny v nátrubku parogenerátoru. Available at various institutes of the ASCR
Posouzení výpočtové dokumentace návrhu opravy heterogenního svárového spoje nátrubku PG technologií Weld Overlay. Dokumentace k výpočtovému modelu MKP pro hodnocení kritické velikosti trhliny.

V první cásti zprávy je vypracováno posouzení výpoctové dokumentace návrhu opravy heterogenního svarového spoje nátrubku superhavarijního napájení parogenerátoru v JE Dukovany technologií Weld Overlay ...

Pták, Svatopluk; Masák, Jan; Gabriel, Dušan
Ústav termomechaniky, 2017

Optimalizace výběru senzorů pro lokalizaci zdrojů akustické emise
Chlada, Milan; Převorovský, Zdeněk
2017 - Czech
Podobně jako v případě globálního polohového systému (GPS) se v případě lokalizace materiálových defektů metodou akustické emise (AE) setkáváme s efektem tzv. snížení přesnosti vlivem geometrie (GDOP). Kromě možností stávajících přístupů k analýze a porovnání různých konfigurací senzorů z hlediska přesnosti lokalizace přináší nově navržená metoda další výhody při detekci kritických oblastí charakterizovaných velkou citlivostí k chybám určení začátků signálů. Analogicky k parametru GDOP umožňuje výpočet tzv. citlivostních map i pro případy nespojitých těles, či anizotropních materiálů. Vychází z algoritmu hledání nejkratších cest v diskrétně zadaných tělesech, což generuje další náhledy na problematiku skrze podobnostní mapy a schémata nejednoznačností. Similarly to Global Positioning System (GPS), location of material defects by acoustic emission method meets the geometrical dilution of precision (GDOP) phenomena. Besides the several attitudes how to mathematically express its measure and compare particular sensor configurations in accordance with desired location precision, recently proposed method brings extended possibilities for detection of critical regions characterized by strong sensitivity of location results to signal arrival time changes or errors. Analogically to GDOP parameter it yields the sensitivity map available even for non-continuous or anisotropic materials. During the computation it uses the algorithm for finding the shortest ways in discretely defined bodies, which furthermore enables to view the problem through the so-called similarity and ambiguity maps. Keywords: acoustic emission; source location; geometrical dilution of precision Available at various institutes of the ASCR
Optimalizace výběru senzorů pro lokalizaci zdrojů akustické emise

Podobně jako v případě globálního polohového systému (GPS) se v případě lokalizace materiálových defektů metodou akustické emise (AE) setkáváme s efektem tzv. snížení přesnosti vlivem geometrie ...

Chlada, Milan; Převorovský, Zdeněk
Ústav termomechaniky, 2017

Lokalizace zdrojů spojité akustické emise pomocí časové reverzace signálů
Převorovský, Zdeněk; Krofta, Josef; Kober, Jan; Chlada, Milan
2017 - Czech
V příspěvku je navržena nová metoda lokalizace akustické emise (AE) využívající proceduru časové reverzace signálů (TR – Time Reversal) s jedním snímačem pro lokalizaci pulzní AE na šumovém pozadí z jiných zdrojů, resp. se dvěma snímači pro lokalizaci zdrojů spojité AE (úniků média). TR procedura je zde poprvé aplikována na dlouhé signály s charakterem náhodného šumu. Metoda byla ověřována pomocí simulovaných zdrojů AE na ocelové desce a částech potrubí a výsledky potvrdily její robustnost. Určitou nevýhodou je nezbytnost podrobného skenování předem vymezené oblasti v okolí pravděpodobného výskytu zdroje, kterou je však možné eliminovat např. pomocí rozsáhlejších numerických simulací na počítačovém modelu konstrukce. Přesnost lokalizace kvazibodového zdroje (okolo 1 mm) je lepší než vlnová délka či apertura snímačů. A new solution with the help of Time Reversal (TR) signal processing approach is suggested in this paper. It allows planar location of burst AE sources under high background noise using only one transducer, and continuous AE sources with two transducers, both under high background noise from other sources. TR procedure was in this approach applied to long random noise signals for the first time. Suggested method was verified by means of experimentally simulated AE sources on a steel plate and tube. Source location results certified high robustness of suggested approach. Certain disadvantage of the new method is requirement of detailed scanning of region around a presumed source. Scanning may be eliminated if we use numerical simulations with TR signals put into a computer model of the structure. Localization accuracy of suggested procedure (approx. 1 mm) is better than the wavelength and transducers aperture. Keywords: burst and continuous AE on; leakage location; time reversal acoustics Available at various institutes of the ASCR
Lokalizace zdrojů spojité akustické emise pomocí časové reverzace signálů

V příspěvku je navržena nová metoda lokalizace akustické emise (AE) využívající proceduru časové reverzace signálů (TR – Time Reversal) s jedním snímačem pro lokalizaci pulzní AE na šumovém pozadí z ...

Převorovský, Zdeněk; Krofta, Josef; Kober, Jan; Chlada, Milan
Ústav termomechaniky, 2017

Numerical Simulation of Laminar-Turbulent Transition in Accelerated Flows
Fürst, J.; Příhoda, Jaromír
2017 - English
The article deals with the evaluation of two RANS based models for simulation of transitional flows including heat transfer. The work is focused on the transition and heat transfer in cases of accelerated flows over a flat plate and through a test turbine cascade. Keywords: turbulence; laminar-turbulent transition; finite volume method Fulltext is available at external website.
Numerical Simulation of Laminar-Turbulent Transition in Accelerated Flows

The article deals with the evaluation of two RANS based models for simulation of transitional flows including heat transfer. The work is focused on the transition and heat transfer in cases of ...

Fürst, J.; Příhoda, Jaromír
Ústav termomechaniky, 2017

Simulation of Transonic Flow Through a Mid-Span Turbine Blade Cascade with the Separation-Induced Transition
Straka, P.; Příhoda, Jaromír; Fenderl, D.
2017 - English
The paper deals with the numerical simulation of the transonic flow through a mid-span turbine blade cascade by means of an in-house code based on the EARSM turbulence model of Hellsten [1] completed by the algebraic transition model of Straka and Příhoda [2]. The simulation using the transition model of Langtry and Menter [3] and Menter et al. [4] implemented in the commercial code ANSYS Fluent was used for the comparison. Simulations were carried out for the transonic regime close to the nominal regime. The flow separation on the suction side of the blade is caused by the interaction of the reflected shock wave with the boundary layer. The attention was focused on the modelling of the transition in the separated flow especially on the modelling of the length of the transition region. Numerical results were compared with experimental results. Keywords: mid-section blade cascade; boundary layer transition; shock wave interaction Fulltext is available at external website.
Simulation of Transonic Flow Through a Mid-Span Turbine Blade Cascade with the Separation-Induced Transition

The paper deals with the numerical simulation of the transonic flow through a mid-span turbine blade cascade by means of an in-house code based on the EARSM turbulence model of Hellsten [1] completed ...

Straka, P.; Příhoda, Jaromír; Fenderl, D.
Ústav termomechaniky, 2017

Analysis of non-harmonic excitation of synthetic jet actuators
Kordík, Jozef; Trávníček, Zdeněk
2017 - English
Axisymmetric synthetic jet actuator based on a loudspeaker was tested experimentally. The actuator was driven by a voltage waveform, whose shape was derived from a pulse-width modulated signal. While the duty cycle and frequency of the excitation signal were varied the outlet velocities were measured by a hot-wire probe. Integral quantities such as characteristic velocity, momentum flux, and kinetic energy flux were evaluated from the outlet velocities. Their maxima were located as functions of frequency and the duty cycle. The found maximal values were compared with results obtained for harmonic excitation. The highest improvement (about 18%) was achieved for kinetic energy flux. Keywords: synthetic jet; synthetic jet actuator; momentum flux Available at various institutes of the ASCR
Analysis of non-harmonic excitation of synthetic jet actuators

Axisymmetric synthetic jet actuator based on a loudspeaker was tested experimentally. The actuator was driven by a voltage waveform, whose shape was derived from a pulse-width modulated signal. While ...

Kordík, Jozef; Trávníček, Zdeněk
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; experimental simulation of human phonation in vitro 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

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