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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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Generation of small water droplets
Tesař, Václav
The task was to generate and supply into flowing biogas very small water sroplets, substantially smaller than the width 0,3 mm of the gaps through which the biogas has to flow. The requested water flow rate is very small, 7.15 10-6 kg/s (25.7 g/hr). Author performes analysis of abailable alternative droplet generation mechanisms as follws:1) Forcing the water to flow through a small nozzle, alternatively with a fluidic oscillation generator2) Pneumatic generation, for which theoretical groundwork was assembled from linerature,3) Rotational centrifugal method4) Condensation method5) Ultrasonic generator.The last named method was found to be practically most suitable.
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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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Experimental study of a control synthetic jet's efficiency
Němcová, L. ; Kopecký, V. ; Trávníček, Zdeněk
The present paper deals with an active control of jet flows by means of a system of synthetic jets. The control synthetic jet in one segment of the main round nozzle was measured by means of PIV. The strength of the control synthetic jet was quantified, relatively to the main jet, in terms of the ratios of their velocities, flow rates, and momenta. The results confirm efficiency of the present flow control method.
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