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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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LITTLE KNOWN PRINCIPLES OF FLUIDIC PUMPING
Tesař, Václav
The paper present a survey of possibilities offered by fluidics in pumping liquids - especially hazardous ones. With its absence of moving,deformed, or sealed components, fluidics offers extraordinary safety, robustness, resistance to extreme conditions, no maintenance and the extraordinary property of transferring the pumping power across a completely closed containment barrier.Initially developed for the extreme conditions of nuclear fuel re-processing, fluidic pumps can be useful – but remain so far little known outside of this area.
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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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No-Moving-Part Two-Regimes Control of an Airfoil Cascade
Tesař, Václav
Airfoil cascades are essential parts of energy converting machines. The paper discusses a new concept of flow control in the cascade, inspired by fluidic amplifiers based on the Coanda effect. In place of mechanically articulated blades, the airfoil properties are controlled by auxiliary flow issuing from a slit nozzle in the blade. The alternate attachment to either one of a pair of attachment walls results in two alternative flow regimes. Several applications are discussed in detail, mainly concentrating on a cascade controlling the entrance flow into the vortex chamber of a turn-down flow control valve.
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PIV investigations of an excited air jet
Tesař, Václav ; Uruba, Václav ; Něnička, Václav
Authors investigated an axisymmetric jet of air issuing from a 40 mm dia. nozzle using 3D particle image velocimetry system. The jet was excited by a rotating acousticpressure field in the nozzle exit plane to ensure generation of two helical instability modes chasing one another and mutually interacting. The excitation signal was also used for ensuring PIV data acquisition at a precise phase position
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Turbulence spectra evaluation using a similarity model
Tesař, Václav ; Kordík, Jozef
Authors measured instantaneous velocities in points along the axis of a synthetic jet and evaluated there the spectral density of the measured values. Analysis of these spectra necessitates knowledge of quantities - such as the dissipation rated of eddies – difficult to evaluate and usually not know. In the present case they were found from to the earlier performed fit to quasi-similarity solution of the flowfield, based upon the one-equation model of turbulence.
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Processing flow visualisation records by correlation coefficient evaluation in sub-images
Tesař, Václav ; Něnička, Václav
Authors introduced a new method of processing flow visualisation images,aiming at identification of instability structures. In principle, the method utilises the structures' coherence. In two digital images, recorded at slightly differentinstants of time, the pixel pairs from the same position in the images are interrogated one by one. In each, vectors of the recorded quantity values are formed from n x n pixels in immediate neighbourhood, which form the sub-image. The correlation coefficient is then computed for the vector pair. High positive values of the coefficient indicate absence of change whereas values near zero indicate chaotic changes. Of interest are negative values, which indicate a coherent motion.
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Studie fluidických snímačů rychlosti útku
Tesař, Václav
Měření rychlosti axiálního nestacionárního pohybu útku v tlakcovském bezčlunkovém stavu se jevilo jako neuskutečnitelné. Řešení autor nalezl využitím principu kolize vzduchových proudů. V příspěvku je popsán další vývoj a hledání jiných principů, zaměžené na dosžení vyšší citlivosti bezkontaktního fluidického snímání.
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