|
|
Collision of a Small Bubble with a Large Falling Particle
Vejražka, Jiří ; Hubička, M. ; Basařová, P.
The motion of a tiny bubble (< 1mm) in a neighborhood of a solid sphere falling through a liquid is studied. A model assuming irrotational flow around the sphere and spherical bubble shape is provided; this model is validated by comparison with the experiment. The model can be further simplified by neglecting inertial forces, which are negligible in present experiments. Results of the model are provided also for the opposite limit, in which the inertial forces are dominating the bubble motion.
Plný tet: SKMBT_C22014011511310 -  PDF
Plný text: content.csg - PDF
|
|
|
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.
Plný tet: SKMBT_C22012112614031 - PDF
Plný text: content.csg - PDF
|
|
|
The Transitional Regime of Backward-Facing Step Flows
Tihon, Jaroslav ; Pěnkavová, Věra ; Havlica, Jaromír ; Šimčík, Miroslav
The backward-facing step flow is investigated experimentally (electrodiffusion technique) and numerically (CFD software Fluent) at moderate Reynolds numbers achieved in a water channel. The direction sensitive sensors are used to measure the wall shear rate behind the step and detect the near-wall extent of different flow-recirculation regions. 2D numerical simulations provide additional information on the global flow rearrangement caused by the change of operational parameters (channel expansion ratios, inlet flow conditions). At the transitional flow regime, the near-wall flow exhibits an unsteady character with a high sensitivity to external low-frequency perturbations (intrinsic flow instability). The inlet pulsatile forcing is found to affect strongly the overall flow structure behind the step, resulting in the reattachment length reduction and the reverse flow intensification.
|
|
|
Oscilace bublin a kapek přichycených na jehle
Vejražka, Jiří ; Vobecká, Lucie
Práce uvádí výpočetní postup pro stanovení vlastních frekvencí, tvarů a příslušných útlumů pro tvarové kmitání bubliny nebo kapky přichycené na jehle. Výpočetní postup je založen na analýze Bostwicka a Steena, jehož výsledek je algebraicky upraven do kompaktního tvaru. Výsledky výpočtu vykazují dobrou shodu s experimentem, pokud je velikost bubliny dostatečně menší než velikost při odtrhu vlivem Archimedových nebo gravitačních sil.
Plný text: PDF
|
host ::
RSS.