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Spectral analysis of continual and synthetic jet
Broučková, Z. ; Trávníček, Zdeněk ; Šafařík, P.
This experimental work deals with a characterization of three types of air jet flows (continual jet, synthetic jet and continual jet which is controlled by a synthetic jet). The characterization is performed using the power spectral density (PSD). All the characteristics were obtained from single-point measurements of flow velocity. The velocity was measured by a hot-wire anemometer (CTA). Power spectral density was acquired directly from measured signal (or from velocity data) by means of MATLAB software. Obtained graphs showed the control effect on the main flow behaviour. The significant qualitative change was revealed near a boundary of synthetic jet formation. Moreover it was concluded that this significant change can be also well quantified.
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Visualization of the flow around rotating cylinder
Broučková, Z. ; Trávníček, Zdeněk ; Šafařík, P.
The visualization of the flow around a rotating and standing cylinder has been performed in air. This visualization has been performed for two velocities of a freestream for Reynolds numbers Re = 920 a 990 and for four frequencies of the rotation (0 s-1, 5 s-1, 12.5 s-1 and 20 s-1). The results have been compared with the theoretical model – potential flow. The velocity of the freestream has been evaluated by measurement of the frequency of the shedding vortices behind the standing cylinder in the regime of the Kármán vortex street. In the regime of the Kármán vortex street the Reynolds numbers were Re = 110 a 120. The known relations between Stouhal and Reynolds numbers were used.
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Region of parameters of synthetic jets
Broučková, Z. ; Šafařík, P. ; Trávníček, Zdeněk
This work presents a summary of parameters which are needed for the descriptionof synthetic jets. Examples from available literature are discussed. A reliability of severalformation criteria of these jets is also verified. Most of the criteria have similar character andgive reliable results - all chosen examples satisfy the criteria. It is shown that one of theinvestigated criteria is not very trustful.Furthermore, the measurements of velocity of the axisymmetric synthetic jet were performedby means of the Pitot tube and the Hot-Wire Anemometry. The results are in very goodaccordance with the ones from literature. Moreover, it was revealed that the decreasing of theReynolds number and the working point approaching towards the critical value on theboundary of formation lead to the gradual shortening of the reach of the jet.
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Visualization of synthetic jets at higher stokes numbers
Broučková, Zuzana ; Trávníček, Zdeněk ; Šafařík, Pavel
Visualization of synthetic jets at higher Stokes numbers (S = 90 and 127) by the phase-locked smoke-wire technique is presented and discussed. The working fluid is air. The Reynolds numbers are quantified using hot-wire anemometry. Although our method of visualization essentially provides only qualitative results, the present study also demonstrates some quantitative results, namely the behavior of the zero-net-mass-flux jet near its critical stage. Visualization of the sub-critical stage is also shown.
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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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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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