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Stochastic regimes in very-low-frequency fluidic oscillator
Tesař, Václav
Paper discusses interesting unexpected stochastic regimes discovered in a fluidic oscillator designed for operation at very low oscillation frequencies - without the inconvenience of the long feedback loops needed in standard low-frequency oscillator designs. The new oscillator contains a pair of bistable turn-down active valves operating in anti-parallel — essentially analogous to Abraham & Bloch electric “multibrateur” invented in 1919. Three different self-excited oscillation regimes were found. In the order of increasing supplied flow rate, these regimes are characterised by: (A) generation of stochastic-duration multi-pulse packs, (B) generation of individual pulses with a degree of periodicity, and (C) regime with randomly appearing flow pulses separated by intervals of the order of seconds.
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Fluidic low-frequency oscillator consisting of load-switched diverter and a pair of vortex chambers
Tesař, Václav ; Peszyński, K. ; Smyk, E.
Paper discusses a new configuration of fluidic oscillators, a subject of recent Patent application. There is some similarity with the standard Warren oscillator with its bistable jet-deflection diverter and two feedbacks – which is not suitable for situations demanding very low oscillation frequency. For these conditions the new design replaces jet-deflection switching in the diverter by load-switching effects, with the gradually increased loading by spin-up of fluid in the vortex chambers. The spin-up time also provides the needed time delays. Behaviour is characterised by the oscillation frequency increasing with increasing fluid flow rate – for which was derived a surprisingly simple theoretical solution.
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Colloquium Fluid Dynamics 2014
Jonáš, Pavel ; Uruba, Václav
Selected results on theoretical and experimental fluid mechanics research at academic institutes, universities and other research and development establishments are presented in Colloquium Fluid Dynamics 2014 Proceedings. Seventeen contributions refer to the flow equations solutions, numerical calculations, flow visualization, investigations of shear flows dynamics, laminar turbulent transition, visualization in superfluid 4He, aerodynamic testing of supersonic blade cascades, fluidic oscillator etc.
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Atomiser with excitation by a fluidic oscillator
Tesař, Václav ; Hykl, Jiří
Paper summarises results obtained in preliminary feasibility study of a novel pneumatic atomiser for generation o fine droplet spray. The new feature is pulsating the air supply by means of a no-moving-part fluidic oscillator. Tests involved recording by high-speed camera and optical measurements of the droplet size by laser light scattering and suggested a promising future potential necessitating, however, further development and optimisation.
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Preventing microbubble conjunctions by gas flow excited by a fluidic oscillator
Tesař, Václav
Recently demonstrated was efficient generation of desirable small-size microbubbles in liquids by applying oscillation to the air flow supplied into the aerator - preferably by means of a simple and inexpensive fluidic oscillator. It remained unexplained what the oscillation actually does with the bubbles. In this paper was established that microbubbles are produced in a process consisting of several discrete steps, in each growing in size. Oscillation of the gas flow can eliminate this growth and keep the resultant bubbles small. Two alternative mechanisms were identified than can suppress the growth.
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Nestacionární charakteristiky impaktního proudění do korýtkové kavity
Knob, Martin ; Antoš, Pavel ; Adamec, J.
In this contribution, the unsteady behaviour of a jet, impinging into a trough cavity is described. The mechanism of the switching of the jet is clarified and the effect of the impingement angle is discussed. The problem was studied both experimentally and numerically. The numerical investigation is performed using a commercial package Fluent 6.1, while the experimental data are obtained using the hot- wire probe. The experimental and the numerical data are compared and discussed.
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