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Comparison of holographic setups used in heat and mass transfer measurement
Doleček, Roman ; Psota, Pavel ; Lédl, Vít ; Vít, Tomáš ; Kopecký, V.
The authors of the paper deal with measurement of heat and mass transfer for several years and they have frequently used few techniqes for measurement of refractive index distribution based on holographic interferometry. Some of the well known techniques have been modified some and some new ones developped. Every technique could be applied with success in different type of meassurement and obviously every one has set of properties making them unique. We decided to digest few different basic techniques and describe its properties in this paper with the aim to help the reader select the proper one for their measurement. The list of techniques and its properties is not comprehensive but schould serve as a basic orientation in the field.
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Numerical experiments modelling turbulent flows
Trefilík, Jiří ; Kozel, Karel ; Příhoda, Jaromír
The paper deals with modification of the transition model with the algebraic equation for the intermittency coefficient proposed originally by Straka and Příhoda (2010) for the bypass transition for modelling of the transition at low free-stream turbulence. The modification is carried out using accessible experimental data for the flat-plate flow. Further, the three-equation k-kL-omega model proposed by Walters and Cokljat (2008) was used for the modelling of the transition at low free-stream turbulence. Both models were tested by means of the incompressible flow around airfoils at moderate and very low free-stream turbulence.
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Modelling of natural and bypass transition in aerodynamics
Fürst, J. ; Straka, P. ; Příhoda, Jaromír
The paper deals with modification of the transition model with the algebraic equation for the intermittency coefficient proposed originally by Straka and Příhoda (2010) for the bypass transition for modelling of the transition at low free-stream turbulence. The modification is carried out using accessible experimental data for the flat-plate flow. Further, the three-equation k-kL-omega model proposed by Walters and Cokljat (2008) was used for the modelling of the transition at low free-stream turbulence. Both models were tested by means of the incompressible flow around airfoils at moderate and very low free-stream turbulence.
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Dynamics of secondary flow behind backward-facing step in a narrow channel
Uruba, Václav
Dynamics of the flow-field behind a backward-facing step in a narrow channel is studied experimentally using time resolved PIV technique. Secondary flow represented by vortical structures is studied using Oscillation Pattern decomposition technique. The low-frequency quasi-periodical structures appearing in the region just behind the step close to the channel bottom are studied. Typical dynamics of vortex structures involving contra-rotating vortex pair train, vortices coalescence and splitting have been observed.
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Physical principle dealing with development of vortices formed by DBD actuator
Procházka, Pavel P. ; Uruba, Václav
Several configurations of vortex trains generated by plasma dielectric barrier discharge were measured by method of time-resolved PIV with application of phase-averaging of data. Mainly dynamics of vortical structures was studied in terms of vortex core trajectory, convective velocity, vortex diameter and vortex circulation. The generally valid physical mechanism of such vortices based on gained information will be introduced and presented. This mechanism will be considered with regards to the use for active flow control thus it could be very helpful in the future works dealing with plasma flow control.
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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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Comparison of heat transfer in straight and corrugated minichannels with two-phase flow
Peukert, P. ; Hrubý, Jan
Measurements of heat transfer rates performed with an experimental condensation heat exchanger are reported for a corrugated minichannel tube and for a straight minichannel tube. The two cases were compared at same flow regimes. The corrugation appears advantageous for relatively low steam pressures and flow rates where much higher heat transfer rates were observed close to the steam entrance, thus allowing shortening the heat exchanger with the associated advantages of costs lowering and smaller built-up space. At high steam pressures and high flow rates both tubes performed similarly.
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