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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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Velocity spectra and transition into turbulence in synthetic jets
Tesař, Václav
Paper investigates transition into turbulence in synthetic jet. The investigation was based on the quasi-similarity model with model parameter varying along the jet trajectory.The distance travelled from the nozzle to the location of the transition depends on the driving frequency – and hence on the size of the vortical structures, which were modelled by a sphetical vortex model. It appears the trasnsition takes placeat the distance equal to ~20 diameters of this model object.
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HYBRID-SYNTHETIC IMPINGING JETS
Tesař, Václav
Impinging jets can achieve the highest convective heat or mass transfer rate. An increase beyond present limits is possible by pulsation of the flow. The extreme case of the synthetic jets could be particularly effective – were there not the re-ingestion of the fluid. A solution brings the new concept of non-zero time mean hybrid synthetic jet.
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The interaction of continual and synthetic jets
Broučková, Zuzana ; Trávníček, Zdeněk ; Šafařík, Pavel
This work deals with an interaction of continual and cross synthetic jets. Both jets are axisymmetric. All measurements have been performed in air by means of the Pitot tube and hot-wire anemometry. Flow visualization has been also performed. The possibility of flow control is shown and quantified. For the moderate momentum ratio, the mean jet deflection reasonably agrees with the momentum conservation.
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GENERACE MALÝCH VODNÍCH KAPIČEK
Tesař, Václav
Úlohou bylo generovat a dodávat do proudícího bioplynu velmi malé vodní kapičky, podstatně menší než šířka 0,3 mm mezer, kterými bioplyn proudí. Požaduje se velmi malý maximální průtok vody 7.15 10-6 kg/s (25.7 g/hod). Autor provedl rozbor použitelných alternativních mechanismů generace kapiček: 1) Protlačování vody výtokovou tryskou, případně s fluidickým generátorem oscilací, 2) Pneumatická generace, pro níž byly z literatury shromážděny teoretické podklady. 3) Rotační odstředivá metoda. 4) Kondenzační metoda. 5) Ultrazvukový generátor. Poslední metoda se ukázala jako prakticky nejvhodnější.
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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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