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Experimental investigation of a control synthetic jet
Němcová, L. ; Kordík, Jozef ; Trávníček, Zdeněk ; Kopecký, V.
Synthetic jets were used in previous studies to control a continuous round air jet. This study focuses on the single synthetic jet, which is measured using Constant Temperature Anemometry (CTA) and Particle Image Velocimetry (PIV). Velocity profiles and frequency characteristics of the single synthetic jet are discussed and the velocity maps at frequencies of 30 Hz, 81 Hz and 190 Hz are presented. Finally, velocity, flow rate and momentum coefficients featured the present flow control are evaluated, and examples of actively controlled round air jet are put on. The results confirm efficiency of the present flow control method.
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AXIAL VARIATION OF A SYNTHETIC JET FREQUENCY SPECTRUM
Tesař, Václav ; Kordík, Jozef
Frequency spectra of synthetic jets vary along the jet axis and there is sudden change of the character and structure of axisymmetric synthetic jets at the relative axial distance from the virtual origin X1*/d ~50. Processing the spectra into the compensated form made obvious a number of surprising facts – one of them the discovery that what wasexpected to be the Komogorov constant obviously varies quite significantly along the jet, its variations exhibiting a marked change in its behaviour at the critical transition.
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Turbulence spectra evaluation using a similarity model
Tesař, Václav ; Kordík, Jozef
Authors measured instantaneous velocities in points along the axis of a synthetic jet and evaluated there the spectral density of the measured values. Analysis of these spectra necessitates knowledge of quantities - such as the dissipation rated of eddies – difficult to evaluate and usually not know. In the present case they were found from to the earlier performed fit to quasi-similarity solution of the flowfield, based upon the one-equation model of turbulence.
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Active control of an annular jet by means of the radial synthetic jet
Broučková, Zuzana ; Kordík, Jozef ; Trávníček, Zdeněk
This experimental study deals with an annular jet, which is actively controlled. Firstly, the following partial tasks were measured: axisymmetric continual jet, axisymmetric synthetic jet, radial synthetic jet, and annular jet without control. Measurement was performed in air by means of the Pitot probe and hot-wire anemometer. The results of partial steady tasks confirm knowledge, available from literature. The expected resonant behavior of the synthetic jet actuators was confirmed too. A possibility of flow control of the mean annular jet was proved. A suitable frequency and amplitude of the control synthetic jet was 600Hz and 23m/s, respectively.
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Termoakustický prime mover – demonstrace a prvotní experimenty
Chen, Y.-Ch. ; Vít, Tomáš ; Lédl, V. ; Kordík, Jozef ; Maršík, František ; Wang, A. B. ; Doleček, R. ; Trávníček, Zdeněk
The present paper focuses on an experimental investigation of the thermoacoustic prime mover (sound generator), which was designed with the quarter-wave resonant tube. The working fluid was air under the barometric pressure. This study proves function of the prime mover, and demonstrates variety of experimental methods for experimental investigation of the thermoacoustics: acoustic measurements (the resonant frequency, power spectrum, and sound pressure level), temperature measurement (temperatures along the resonant tube, namely near the thermoacoustic stack), hot-wire measurement (oscillation velocities and displacements), and optical experiments by the holographic interferometry.
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Systematické vyšetřování vzdáleného rychlostního pole syntetizovaných proudů
Tesař, Václav ; Kordík, Jozef
Paper presents results evaluated from anemometric data on a large number of synthetic jets. The results are based on a one-equation turbulence model solution of time-mean synthetic jets. This solution follows the classical concept of similarity transformation, but depends on a parameter the value of which varies along the jet axis. This is idea has been there before, but the scarcity of so far available experimental data made the previous attempt unreliable. This is now improved by the large number of new data that correct some previous coclusions.
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