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Numerical experiments for turbulent flows
Trefilík, Jiří ; Kozel, Karel ; Příhoda, J.
The aim of the work is to explorethe possibilities of modelling transonic flowsin the internal and external aerodynamics. Several konfigurationswere analyzed and calculations were performed using both inviscid and viscous models of flow. Viscous turbulent flows have been simulated using either zero equation algebraic Baldwin-Lomax model and two equation k - w model in its basic version and improved TNT variant. The numerical solution was obtained using Lax-Wendroff scheme in the MAcCormack from on structured non-ortogonal grids. Artificial dissipation was added to improve the numerical stability. Achieved results are compared with experimental data.
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LDA measurements and turbulence spectral analysis in an agitated vessel
Kysela, Bohuš ; Konfršt, Jiří ; Chára, Zdeněk
During the last years considerable improvement of the derivation of turbulence power spectrum from Laser Doppler Anemometry (LDA) has been achieved. The irregularly sampled LDA data is proposed to approximate by several methods e.g. Lomb-Scargle method, which estimates amplitude and phase of spectral lines from missing data, methods based on the reconstruction of the auto-correlation function (referred to as correlation slotting technique), methods based on the reconstruction of the time series using interpolation between the uneven sampling and subsequent resampling etc. These different methods were used on the LDA data measured in an agitated vessel and the results of the power spectrum calculations were compared. The measurements were performed in the mixing vessel with flat bottom. The vessel was equipped with four baffles and agitated with a six-blade pitched blade impeller. Three values of the impeller speed (Reynolds number) were tested. Long time series of the axial velocity component were measured in selected points. In each point the time series were analyzed and evaluated in a form of power spectrum.
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Wall Shear Stress Induced by Taylor Bubbles in Inclined Flow Channels
Tihon, Jaroslav ; Pěnkavová, Věra ; Vejražka, Jiří
The motion of single air bubbles in flat channels is experimentally investigated. The electrodiffusion technique of near-wall flow diagnostics is applied to measure the wall shear stress distribution under large rising bubbles. The measurements are synchronized with the visual observation of bubble movement by a high-speed camera. The analysis of video records provides information on the bubble shape and terminal velocity. The experiments are carried out for three different channel configuration (with heights of 1.5, 4, and 8 mm), cover a wide range of channel inclination angles (from horizontal to vertical position), and dealing with both the bubbles in stagnant and in co-flowing water.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22012112614030 - PDF
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Oscillations of Bubbles Attached to a Capillary: Case of Pure Liquid
Vejražka, Jiří ; Vobecká, Lucie ; Tihon, Jaroslav
In this contribution, we therefore present results of a linear inviscid theory for shape oscillations of a spherical bubble, which is in contact with a solid support. The theory allows determining eigenmode, but also response of the bubble shape to a motion of its support or to volume variations. Present theory covers also the cases previously analyzed by Strani and Sabettaand Bostwick and Steen, and it can be applied to both bubbles and drops. The theory has been compared to experiments. Good agreement is found for the case of small bubbles, which have spherical static shape. Experimental results for larger bubbles and drops deviate from the theory, if a neck is formed. It is shown that this deviation correlates well with a ratio of bubble volume to the maximum volume, when a detachment occurs.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22012112614031 - PDF
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