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Vortex dynamics of a suddenly arrested cylinder
Chára, Zdeněk ; Kysela, Bohuš
Results from an experimental study of the flow generated by a cylinder immersed in fluid, suddenly arrested or impacting normally without rebound on a solid wall, are presented. The trajectory of both the wake vortices, as well as the secondary vortices induced as the original wake convects over the arrested cylinder were investigated.
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Estimation of turbulence dissipation rate by Large eddy PIV method in an agitated vessel
Kysela, Bohuš ; Jašíková, D. ; Konfršt, Jiří ; Šulc, R. ; Ditl, P.
The distribution of turbulent kinetic energy dissipation rate is important for design of mixing apparatuses in chemical industry. Generally used experimental methods of velocity measurements for measurement in complex geometries of an agitated vessel disallow measurement in resolution of small scales close to turbulence dissipation ones. Therefore, Particle image velocity (PIV) measurement method improved by large eddy PIV approach was used. Large eddy PIV method is based on modeling of smallest eddies by a sub grid scale (SGS) model. This method is similar to numerical calculations using Large Eddy Simulation (LES) and the same SGS models are used. In this work the basic Smagorinsky model was employed and compared with power law approximation. Time resolved PIV data were processed by Large Eddy PIV approach and the obtained results of turbulent kinetic dissipation rate were compared in selected points for several operating conditions (impeller speed, operating liquid viscosity).
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Numerical simulations of flow over stationary deposit
Chára, Zdeněk ; Vlasák, Pavel ; Kysela, Bohuš ; Konfršt, Jiří
The paper deals with a water flow in a horizontal, circular pipe of inner diameter 40 mm with a stationary deposit. The deposit was formed by spheres of diameter d=6 mm. The thickness of the deposit was about two sphere diameters. The flow was experimentally studied by the PIV method and COMSOL Multiphysics 4.4 was used as tool for numerical simulations as well. Two approaches were used to create the stationary deposit. In the first one was the deposit was replaced by a rough wall with different values of the roughness parameter ks. In the second case the deposit was created from the identical spherical particles. The results of the simulations and the experimental data are compared.
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Comparison of measured instantaneous velocities and a calculated flow in an agitated vessel
Kysela, Bohuš ; Pešava, V. ; Konfršt, Jiří ; Chára, Zdeněk ; Kotek, M.
Proces míchání je řízen změnami rychlostního pole a tvorbou vírových struktur v průběhu pracovního cyklu. V této studii porovnáváme výsledky CFD výpočtů s výsledky měření střední prostorově průměrované rychlosti, a také polohově závislé rychlosti odpovídající otáčivému pohybu míchadla, při kterém vznikají vírové struktury. Experimentální data časových řad dvourozměrných vektorových map rychlostí byly získány pomocí TR PIV měření v oblasti míchadla. Pro získání hodnot okamžitých rychlostí a vírových struktur bylo použito modelování pomocí LES v kombinaci s SM simulací pohybu oblasti s míchadlem. Získané výsledky jsou zde porovnány a aplikace použité metody diskutována.
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Fine set-up of the Ar-Ion laser and fibre loader
Konfršt, Jiří ; Kysela, Bohuš ; Chára, Zdeněk
Use of lasers in the measuring systems, which use LDA/PDA devices, expects good knowledge of physical characteristics of used light source namely for multicomponent measurements. This article is focused on the experimental parameter analysis of individually separated light wavelength from Ar-Ion plasma tube, working in multiline “ML” mode. The best laser source parameters: aperture size, power input and quality of the utilized separate wavelengths were obtained and beams were adjusted to the optical fibres.
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