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Proposal for an electro/fluidic transducer based on wall-jet separation from a heated curved surface
Tesař, Václav
Transducers for converting electric input signals into a change of flow rate in a fluidic device are increasing in importance – and yet there is no fully satisfactory design solution. Standard two-stage approach is to perform in the first stage a conversion into a motion of a movable (or deformable) mechanical component. Then in the second stage the mechanical effect acts on the fluid flow. Mechanical components complicate manufacturing, have tendency to get stuck or worn – or, in the case of elastic support, to endanger reliability by breakages (e.g. due to material fatigue). Their inertia limits the frequency range. Author proposes an apparently not yet applied idea of transducer containing no moving or deformed parts. The electric input heats a surface to which an air jet is attached, causing its separation. Preliminary experiments show that relatively small heating suffices to change substantially the flowfield — and the reduction of the attachment wall to a thin metal foil can make the frequency range of responses quite acceptable.
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Induced fluid rotation and bistable fluidic turn-down valves (a survey)
Tesař, Václav
Paper discusses engineering applications of mutual interaction between fluid flow rotation in adjacent cavitiesthat communicate via a window through which is transferred moment momentum. The transfer may be merely byshear stress on the interface or enhanced by some flow crossing the boundary which is in the window. The first case of zero-time-mean mass transport through the window has led to methods of measuring the wall shear stress – a quantity of high importance in theoretical fluid mechanics – by measuring the speed of induced rotation in an adjacent vortex chamber. The case with momentum transfer by a non-zero flow became the starting point of development of fluidic valves combining two properties otherwise mutually incompatible: bistability on one side and turning-down the flow on the other side.
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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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Vliv zakřivení stěny na vývoj stěnového proudu
Příhoda, Jaromír
V příspěvku jsou uvedeny výsledky experimentálního vyšetřování vývoje stěnového proudu na kruhovém válci při různé velikosti štěrbiny h/R a Reynoldsova čísla Reh menší než 5000. Tloušťka a maximální rychlost stěnového proudu závisí nejen na vzdálenosti od štěrbiny a na poměru h/R ale i na Reynoldsově čísle Reh.
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