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Small wind tunnel for flow field visualization
Flídr, Erik ; Broučková, Zuzana ; Pavelka, Miroslav ; Trávníček, Zdeněk
This experimental work describes a small wind tunnel for flow field visualization and quantifies its main parameters. Velocity of fluid flow was evaluated by a few experimental methods: - Hot wire anemometry - Videorecord of flow - Velocity measurement at the outlet of the tunnel by hot wire anemometry - Velocity measurement at the outlet of the tunnel by Pitot tube - Continuous velocity measurement at the outlet of the tunnel using the reference Pitot tube Visualization of homogeneous flow field around a circular cylinder was shown.
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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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System for measurement of the heat transfer coefficient
Pavelka, Miroslav ; Trávníček, Zdeněk
This report describes a system, which was developed for measurement of the convection heat transfer coefficient between air and a wall. The system is based on thermopile wall-mounted heat flux sensors. The boundary condition of homogeneous wall temperature is realized by means of an electrically heated wall. System performance was tested for a reference task of an axisymmetric impinging jet. The results were compared with available literature and with another (own, naphthalene sublimation) results. A proper function of the system was confirmed.
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Experimentální studie o matematickém modelování velmi rychlého pneumatického systému
Hrubý, Jan ; Šmíd, Bohuslav ; Pavelka, Miroslav ; Krejčí, A. Petr
We provide some general considerations for design, mathematical modeling, and experimental testing of pneumatic systems with typical transient times of 1 ms. The gas flow is typically critical or near-critical, with significant compressibility effects. We provide a lumped model of a pneumatic system, incorporating the balances of mass, energy and momentum. We show that inertia of the gas plays an important role. For a particular system, designed for application in fundamental research of aerosol particles, we show a reasonable agreement of the lumped model with experimental test of the prototype.
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Frekvenční charakteristika generátoru anulárního syntetizovaného proudu s velkým vnitřním průměrem
Krejčí, A. Petr ; Trávníček, Zdeněk ; Tesař, Václav ; Kordík, Jozef ; Pavelka, Miroslav
An annular synthetic jet actuator of large inner/outer diameter ratio of the nozzle has been developed, and four variants were designed, manufactured, and tested. The resonance frequency was estimated theoretically, based on the mechanical energy balance, and then measured by the pneumometric method. The resultant value was found to be 40 Hz. The nozzle geometry effect on the resonance frequency and on the velocity was quantified; both effects were concluded to be surprisingly small, less than 5%.
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