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Annular Jets and Annular Impinging Jets
Turek, Tomáš ; Trávníček, Zdeněk ; Šafařík, Pavel ; Tesař, Václav
A near field of annular jets and annular impinging jets is experimentally investigated at three inner/outer diameter ratios 0.84, 0.90 and 0.95. Time-mean velocity profiles are evaluated, and three main flow field zones are distinguished – in agreement with the literature, namely the initial merging zone, the intermediate one, and the fully merged one. A distribution of the pressure on the impingement wall is measured for various nozzle-to-wall distances. Two basic annular impinging jet regimes are clearly distinguished, with either small or large recirculation bubbles. Moreover, a hysteretic behavior has been identified under specific parameters.
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High-Frequency, Small-Scale Fluidic Oscillators for Boundary Layer Control
Tesař, Václav
No-moving-part fluidic oscillators are promising candidates for use in jet-type actuators for suppressing the separation in adverse pressure gradient flows and for elmination of the effect of hairpin vortices that absorb the turbulent fluid flow energy. The requests for very high oscillation frequency has led to several new ideas applied to the oscillator configurations.
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“Master and Slave" Fluidic Amplifier Cascade
Tesař, Václav
Paper díscusses mutual matching of two no-moving-part fluidic unvented amplifiers in a two-device module, where small MASTER device, with feedback loop converting it into a small high-frequency oscillator dictates the flow switching in a large powerful SLAVE device. Interest in this configuration was caused by it providing a solution in generation of gas microbubbles. The oscillation frequency has to be high and this calls for small amplifier size - while a the total gas flow has to be large, calling for a large size. The conditions in the circuit is complicated by the need to considerfive terminals in each amplifier.
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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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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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Experimental investigation of synthetic jet array
Dančová, Petra ; Vít, Tomáš ; Kotek, M.
Paper deals on an experimental investigation of a synthetic jet array. This investigation focuses on a partial problem of the general task “a synthetic jet array interacting with a channel flow”. The experiments have been performed with water as a working fluid using hot-wire anemometry, laser Doppler vibrometry and particle image velocimetry methods.
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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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