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Thermoakustic prime Mover – demonstrace a první experimenty
Chen, Y.-C. ; Vít, T. ; Lédl, Vít ; 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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Rezonanční frekvence generátorů syntetizovaných proudů
Kordík, Jozef ; Trávníček, Zdeněk ; Šafařík, P.
This contribution focuses on axisymmetric synthetic jet actuators from the theoretical point of view. In order to evaluate their resonance frequencies, four mathematical models were derived. The results were compared with experimental data, and analyzed. With respect to the theoretical and experimental results, the applicability and limits of the models were discussed. The results illustratively prove correctness of the previous derivation based on transformation of mechanical energy.
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Řízení vztlaku a odtržení na lopatkách vetrných elektrárenúčinkem vírů majících osy orientované ve směru proudění
Tesař, Václav ; Kordík, Jozef ; Daněk, Martin
Paper describes two alternative versions of wind-turbine blade section models for tests in wind tunnel aimed at lift control at high angles of attack. They use synthetic jet (or hybrid-synthetic jet) exiting at 18 % of the chord length on the upper (suction) surface. Otherwise the two layouts are different. In version A the single synthetic jet issues from a continuous exit slit across the full span. In the other version B, a large number of small hybrid-synthetic jets exit in an anti-parallel manner (180 deg phase shift between neighbours) from a row of orifices, switched by an array of small fluidic valves inside the model. Rather surprisingly, despite the differences, the lift control in both layouts was found to be due to generation of vortices with streamwise orientation of their axes.
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Parametry modelu turbulence aplikovaného na syntetizované proudy
Tesař, Václav ; Kordík, Jozef
Anemometric data obtained on two synthetic jets issuing from 4 mm dia nozzle, differing in their frequency (25 Hz and 50 Hz), were applied to one-equation turbulence model solution of jets. It made possible evaluating spatial distributions of unsteady motion in the jets. The classical concept of similarity, however, ceased to be applicable and a concept of quasi-similarity was introduced. An important finding was the discontinuity found in the structure of the unsteady motions – the intial region dominated by large vortices is changed into a region of initially smaller/scale turbulent eddies.
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Vlastnosti trysek – experimentální ověření na zažízení stavěném pro výzkum šroubovicových nestabilit
Tesař, Václav ; Kellnerová, Radka ; Kukačka, Libor ; Kordík, Jozef
Nozzle characterisations in current use may be described as zero-order (neglected loss) and first-order (constant loss coefficient). The first author (V. Tesar) introduced in 1985 a second-order theory, fully predicting all the variations of nozzle properties with Reynolds number Re. The basic idea is an assumption of the loss being entirely specified by displacement effect of wall boundary layer in the exit. The other assumption is the layer thickness being governed by laminar boundary layer growth law. All evidence for this theory so far was only indirect. This paper presents recent direct experimental verification by measurements of boundary layer profiles on a large-scale nozzle model across a wide range of Re. The predictions of the 1985 model are fully supported.
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Frekvenční charakteristika generátoru anulárního syntetizovaného proudu s velkým vnitřním průměrem
Krejčí, A. Petr ; Trávníček, Zdeněk ; Tesař, Václav ; Kordík, Jozef ; Pavelka, Miroslav
An annular synthetic jet actuator of large inner/outer diameter ratio of the nozzle has been developed, and four variants were designed, manufactured, and tested. The resonance frequency was estimated theoretically, based on the mechanical energy balance, and then measured by the pneumometric method. The resultant value was found to be 40 Hz. The nozzle geometry effect on the resonance frequency and on the velocity was quantified; both effects were concluded to be surprisingly small, less than 5%.
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Formation criterion for various synthetic jets: power and frequency characteristics
Kordík, Jozef ; Trávníček, Zdeněk ; Šafařík, P.
Synthetic jets are generated by periodic alternating flows. The jet parameters are: dimension, frequency, oscillation shape and amplitude. The Reynolds number (ReH) and Strouhal number (StH) (or Stokes number SH) are used as dimensionless paramers. The experiment was performed for the Reynolds number range of ReH = 500–10000 and Strouhal number range of StH = 0.2–8.9. Flow visualization and hot-wire measurement were performed. The present results focusing on the jet formation criterion agree quite well with the available literature (the criterion ReH crit = 0.16 SH2).
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Měření přestupu tepla a frekvence oscilací s fluidickým generátorem syntetizovaného impaktního proudu
Tesař, Václav ; Trávníček, Zdeněk ; Kordík, Jozef ; Randa, Zdeněk
The paper discusses recent results of an experimental research of annular impinging hybrid-synthetic jets generated by a no-moving-part fluidic actuator. The actuator is based on a new principle and the first part of the paper discusses the basic configuration idea and the relationship with earlier hybrid-synthetic jet generators. The next part of the paper provides information of a strange phenomenon – an unexpected high-temperature region found on the impingement surface. Also discussed are the measurements of the oscillation frequency. The most important result is the substantial increase of heat transfer efficiency compared with the steady flow from the same nozzles.
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