Number of found documents: 1539
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Generation of Intermittent Jet by Pulse-Modulated Synthetic Jets
Broučková, Zuzana
2018 - English
An axisymmetric air jet was excited using a pair of counter synthetic jets running in opposed direction. First, the control synthetic jets were measured alone. The driving signal was pulse modulated sinusoidal signal. After an adjustment, the primary axisymmetric jet was excited to the bifurcating mode, and its behavior was studied experimentally. For comparison purposes, a reference steady (unforced) jet from the same nozzle was also measured (Reynolds number was approximately 1300). The flow visualization and hot-wire anemometry techniques were used. Keywords: synthetic jet; pulse modulation; flow control Available at various institutes of the ASCR
Generation of Intermittent Jet by Pulse-Modulated Synthetic Jets

An axisymmetric air jet was excited using a pair of counter synthetic jets running in opposed direction. First, the control synthetic jets were measured alone. The driving signal was pulse modulated ...

Broučková, Zuzana
Ústav termomechaniky, 2018

The Influence of Different Geometries of Human Vocal Tract Model on Resonant Frequencies
Valášek, Jan; Sváček, Petr; Horáček, Jaromír
2018 - English
This paper presents the transfer function approach in order to determine the acoustic resonant frequencies of a human vocal tract model. The transfer function is introduced here as an acoustic pressure ratio between input amplitude at glottis position and output amplitude at mouth opening given by the solution of Helmholtz equation. This equation is numerically approximated by finite element method. The influence of different boundary conditions are studied and also different locations of excitation and microphone. \nFour different vocal tract geometries motivated by vocal tract geometry for vowel [u:] are investigated. Its acoustic resonance frequencies in range 100 - 2500 Hz are computed and compared with published results.\nFurther, the transient acoustic computation with different acoustic analogies are performed. The frequency spectra of Lighthill analogy, acoustic wave equation and perturbed convective wave equation are compared, where the vocal tract model with best frequency agreement with published results was chosen. The dominant frequencies correspond with predicted frequencies of transfer function approach.\n Keywords: wave equation; transfer function; aeroacoustic analogies; perfectly matched layer Available at various institutes of the ASCR
The Influence of Different Geometries of Human Vocal Tract Model on Resonant Frequencies

This paper presents the transfer function approach in order to determine the acoustic resonant frequencies of a human vocal tract model. The transfer function is introduced here as an acoustic ...

Valášek, Jan; Sváček, Petr; Horáček, Jaromír
Ústav termomechaniky, 2018

Numerical investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities
Vampola, T.; Štorkán, J.; Horáček, Jaromír; Radolf, Vojtěch
2018 - English
Acoustic resonance characteristics of 3D human vocal tract model without and with nasal and\nparanasal cavities were computed. Nasal cavities (NC) form the side branches of the human vocal tract and exhibit antiresonance and resonance properties which influence the produced voice quality. Developed FE models of acoustic spaces of nasal and vocal tract for vowel /a:/ are used to study the influence of (NC) on phonation. Acoustics frequency-modal characteristics are studied by modal analysis and numerical simulation of acoustic signals in time domain is performed by transient analysis of the FE models. Keywords: formant frequencies; modelling of phonation; biomechanics of voice Available at various institutes of the ASCR
Numerical investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities

Acoustic resonance characteristics of 3D human vocal tract model without and with nasal and\nparanasal cavities were computed. Nasal cavities (NC) form the side branches of the human vocal tract and ...

Vampola, T.; Štorkán, J.; Horáček, Jaromír; Radolf, Vojtěch
Ústav termomechaniky, 2018

Synthetic Jet Characteristic Velocity Estimated nn The Basis of Momentum Flux Measurement
Kordík, Jozef; Trávníček, Zdeněk
2018 - English
The paper compares two methods of evaluation of synthetic jet characteristic velocity. The first method of the characteristic velocity estimation is based on a simple measurement of the synthetic jet momentum flux (the jet thrust) by means of precision scales. The second method is a standard one, it is based on spatial-temporal integration of the velocity profile at the synthetic jet actuator nozzle exit. The velocity profile was obtained here using hotwire measurements in air. Comparison of the methods is based on dimensionless stroke length of the synthetic jet. It is confirmed that the results of both methods are nearly the same for higher dimensionless stroke length. On the other hand, if the jet regime approaches to the synthetic jet criterion threshold (i.e. to the dimensionless stroke length of 0.5) the results of both methods diverge. Using the current results a correction is suggested for the momentum-flux-based method to match the standard one. Keywords: synthetic jet; synthetic jet actuator; momentum flux Available at various institutes of the ASCR
Synthetic Jet Characteristic Velocity Estimated nn The Basis of Momentum Flux Measurement

The paper compares two methods of evaluation of synthetic jet characteristic velocity. The first method of the characteristic velocity estimation is based on a simple measurement of the synthetic jet ...

Kordík, Jozef; Trávníček, Zdeněk
Ústav termomechaniky, 2018

2nd Conference on Ammonia and Greenhouse Gases Emissions from Animal Production Buildings : Book of Extended Abstract
Nosek, Štěpán; Kočí, K.
2018 - English
The texts of the abstracts were set individually by the authors. Any options, findings and conclusions or recommendations expressed in this book are those of the individual authors on their own responsibility. Keywords: livestock; air quality; nutrition; ventilation Available at various institutes of the ASCR
2nd Conference on Ammonia and Greenhouse Gases Emissions from Animal Production Buildings : Book of Extended Abstract

The texts of the abstracts were set individually by the authors. Any options, findings and conclusions or recommendations expressed in this book are those of the individual authors on their own ...

Nosek, Štěpán; Kočí, K.
Ústav termomechaniky, 2018

Experimental investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities
Radolf, Vojtěch; Horáček, Jaromír; Košina, Jan; Vampola, T.
2018 - English
The following experiments were carried out to be later used in the verification of a complex\nmathematical model of human voice production. Acoustic resonance characteristics of a 3D human voca tract model without and with nasal and paranasal cavities were measured in two different ways: The excitation was realized by (1) self-oscillating vocal folds replica and (2) by sine-tone sweeps from an earphone placed instead of the vocal folds. The resulting resonance and antiresonance frequencies were found to be comparable for both excitation signals. Keywords: formant frequencies; modelling of phonation; biomechanics of voice Available at various institutes of the ASCR
Experimental investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities

The following experiments were carried out to be later used in the verification of a complex\nmathematical model of human voice production. Acoustic resonance characteristics of a 3D human voca tract ...

Radolf, Vojtěch; Horáček, Jaromír; Košina, Jan; Vampola, T.
Ústav termomechaniky, 2018

Dynamics of four-planetary gearing box
Půst, Ladislav; Pešek, Luděk; Škuderová, Alena
2018 - English
Planetary gearboxes are more complicated than parallel-axis gear transmission systems and\ntherefore they need deeper dynamic analysis, which is important for reduction of noise and vibration. The main advantage of planetary gearings is the splitting of force flow into several planet wings, but it can be devaluated by unequal load sharing on planet stages. For improving, the floating sun wheal and flexible pins of planets are applied. Dynamic model of such a gearing box is derived in the paper and it is shown that the frequency spectrum contains many multiple eigen-frequencies. Examples of several eigen-modes and transfer functions of this four-planetary gearing box are presented as well. The problem of dimensional nonhomogeneous vectors and matrix is also mentioned. Keywords: planetary gearing; frequency spectrum; multiple eigenvalues; eigen-modes Available at various institutes of the ASCR
Dynamics of four-planetary gearing box

Planetary gearboxes are more complicated than parallel-axis gear transmission systems and\ntherefore they need deeper dynamic analysis, which is important for reduction of noise and vibration. The ...

Půst, Ladislav; Pešek, Luděk; Škuderová, Alena
Ústav termomechaniky, 2018

The influence of permanent magnetic rings on the loss power, vibration and stability of vertical rotors
Zapoměl, Jaroslav; Ferfecki, P.; Sudhakar, A.; Kozánek, Jan
2018 - English
Lifting the vertical rotors by permanent magnets is an advanced technological solution for\nreducing energy losses in the supports. The disadvantage of this design is the instable interaction between the magnetic rings, which may destabilize the rotor oscillations. The performed research was focused on the development of computational procedures for analysis of energy losses in the supports of magnetically lifted vertical rotors mounted in rolling element bearings and on analysis of stability of their vibration in a wide range of operating speeds. The computational simulations proved efficiency of the magnetic suspension. Keywords: lifting vertical rotors; magnetic rings; energy losses reduction; vibration stability evaluation Available at various institutes of the ASCR
The influence of permanent magnetic rings on the loss power, vibration and stability of vertical rotors

Lifting the vertical rotors by permanent magnets is an advanced technological solution for\nreducing energy losses in the supports. The disadvantage of this design is the instable interaction between ...

Zapoměl, Jaroslav; Ferfecki, P.; Sudhakar, A.; Kozánek, Jan
Ústav termomechaniky, 2018

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

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