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Laminární vírová řada za ohřívaným válcem při nerovnoměrném rozložení teploty povrchu
Trávníček, Zdeněk ; Šponiar, D.
Laminar vortex shedding (von Kármán vortex street) of a circular cylinder has been investigated under non-isothermal conditions. Numerical simulation focusing on both fluid dynamics and heat transfer has been performed, and the results were compared with experimental data. Flow was assumed to be two-dimensional, laminar, incompressible or compressible. The working fluid was air. A particular attention was given to simulate various thermal boundary conditions on the cylinder surface. The effect of the type of various thermal boundary conditions on wake flow dynamics and heat transfer was not identified in the present numerical simulations.
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Numerická simulace separovaného dvoufázového proudění vařící se vody v kanálu o tvaru cívky
Novák, Aleš ; Hrubý, Jan
This work deals with a quasi-1D mathematical model of flow of a boiling liquid-vapor mixture in a coil-shaped duct heated from the outer side of the coil. The liquid and gas phases are allowed to flow at different velocities (stratified flow regime). The model simulates a modification of the laboratory steam generator built in Institute of Thermomechanics AS CR. The liquid is centrifuged to the heated wall thus enhancing the heat transfer. The model also includes heat conduction in the metal body of the steam generator.
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Numerická simulace Kármánovy vírové řady za izotermických i neizotermických podmínek
Šponiar, D. ; Trávníček, Zdeněk ; Vogel, J.
This report deals with numerical simulation of the wake airflow behind a circular cylinder using FLUENT solver. The flow is assumed to be two–dimensional, laminar, and incompressible. The Reynolds number ranges Re = 30:-170. The isothermal numerical simulation agree very well with experimental data except the situation near the critical stage (between the steady and vortex shedding regimes); the maximum deviations of simulation and experiments are within 1.2%. The results obtained under the non-isothermal conditions are quite good – except the simulation near the critical stage, where the problems are similar as in the isothermal case.
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Numerical simulation of the von Kármán vortex street
Šponiar, D. ; Trávníček, Zdeněk ; Vogel, Jiří
This report deals with numerical simulation of the wake airflow behind a circular cylinder using FLUENT solver. The flow is assumed to be two–dimensional, laminar, isothermal, and incompressible. The Reynolds number ranges Re = 30÷170. The computations give the steady wake flow for Re = 30÷60 and the periodic vortex shedding (von Kármán vortex street) for Re = 60÷170. The vortex shedding frequency has been quantified in the term of the Strouhal number–Reynolds number relationship. The present results agree very well with the previous experimental data, the maximum deviations of the simulations and experiments are within 1.2%.
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Formation criterion for various synthetic jets: power and frequency characteristics
Kordík, Jozef ; Trávníček, Zdeněk ; Šafařík, P.
Synthetic jets are generated by periodic alternating flows. The jet parameters are: dimension, frequency, oscillation shape and amplitude. The Reynolds number (ReH) and Strouhal number (StH) (or Stokes number SH) are used as dimensionless paramers. The experiment was performed for the Reynolds number range of ReH = 500–10000 and Strouhal number range of StH = 0.2–8.9. Flow visualization and hot-wire measurement were performed. The present results focusing on the jet formation criterion agree quite well with the available literature (the criterion ReH crit = 0.16 SH2).
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Numerická simulace Kármánovy vírové řady
Šponiar, D. ; Trávníček, Zdeněk ; Vogel, Jiří
The wake airflow behind a circular cylinder has been investigated using FLUENT solver. The flow is assumed to be two–dimensional, laminar, isothermal, and incompressible. The Reynolds number ranges Re = 30:-170. The computations give the steady wake flow for Re = 30:-60 and the periodic vortex shedding (von Kármán vortex street) for Re = 60:-170. The vortex shedding frequency has been quantified in the term of the Strouhal number–Reynolds number relationship. The present results agree very well with the previous experimental data, the maximum deviations of the simulations and experiments are within 1.2%.
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Experimentální mechanika tekutin a sdílení tepla a hmoty: strategie výzkumu
Trávníček, Zdeněk
The so-called “Research Strategy” seems to be a typical and quite effective tool for dealing with various problems in Experimental Thermal Fluid Sciences. The working hypothesis is proposed first and then a specific plan is derived from the hypothesis. The problem is divided into manageable parts (step-by-step approach). The purpose of the experiments is to confirm or to reject the hypothesis. The presentation introduces several examples of the recent original results: the influence of the flow structure on heat transfer, passive/active flow control of impinging jets, convective heat transfer enhancement of (steady or pulsatile) impinging jets, synthetic jets, hybrid synthetic jets, stability and bistability of jets, and thermal flow control of wakes. The examples emphasize the role of the discussed methodology, namely the roles of the task motivation, working hypothesis, and interpretation and publication of the results.
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