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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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Colliding wall-jets on a cylindrical surface
Tesař, Václav ; Peszyński, K.
Paper discusses aerodynamics and potential engineering applications of an unusual and in literature practically unknown fluid flow configuration, with two wall-jets attached to a cylindrical surface colliding head-on and generating a single jet directed away. Applications are seen in pneumatic sensors, particularly operating at low Reynolds numbers. Performed experimental investigation combined with numerical flowfield computations revealed several interesting aspects of this flowfield. The most interesting among them is the discovery of symmetry-breaking existence of three different stable flow regimes. This opens a possibility for fluidic tristable amplifiers and control systems operating with ternary logic.
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Fluidic oscillator with bistable turn-down amplifier
Tesař, Václav ; Smyk, E. ; Peszyński, K.
Search for new principles of no-moving-part fluidic oscillators suitable for operation at low frequency – and yet compact – has led to a design based on the amplifier configuration combining bistability (capability to remain in two alternative stable regimes) with capability to turn down the fluid flow passing through it. The feedback was arranged in a manner of recently introduced oscillators with resonator channel. Tests revealed the expected non-constant Strouhal number - but, rather strange, no dependence was found of oscillation frequency on the channel length.
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Control of flow separation by vestigial "synthetic jet"
Tesař, Václav ; Pavelka, Miroslav ; Smyk, E. ; Peszyński, K.
A useful aerodynamic control action may be causing a separation of flow from the wall past which the fluid flows. Several current research activities aim at doing so by oscillating zero-time-mean flow generated in a nozzle located in the wall. The effect is often described as “flow control by synthetic jet”, although it is obvious that the vortex rings generated in the outflow phase of the oscillation are deformed by the controlled flow and also are carried too far away so that they cannot form the classical synthetic jet configuration of vortex rings. Authors describe experiments with such a control applied successfully in an axisymmetric fluidic valve. Presented is a hypothesis explaining the separation mechanism.
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Water oxygenation by fluidic microbubble generator
Tesař, Václav ; Peszyński, K.
Oxygenation of water by standard means is rather ineffective. The classicalapproach to improvements – decreasing the size of the aerator exits - have already reached their limits. Recent idea is to decrease the size of the generated air bubbles by oscillating the supplied air flow using fluidic oscillators. Authors made extensive performance measurements with an unusual high-frequency fluidic oscillator, designed to operate within the submersed aerator body. The performance was evaluated by the dynamic method of recording the oxygen concentration increase to saturation in the aerated water. Experiments proved the fluidic generator can demonstrably increase the aeration efficiency 4.22-times compared with the aeration from a plain end of a submerged air supply tube.
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