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Controlled Production of Bubbles
Vejražka, Jiří ; Stanovský, Petr ; Zedníková, Mária
Two apparatuses for the producing of bubbles with desired volume V and production frequency f are designed. In the first one, the bubble formation is controlled by needle movement and in the second one by changing the chamber volume. Production of bubbles in both devices is modeled using simple model enabling to estimate the range of bubble volumes V and frequencies f, for which the devices will work properly.
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Vortex Structures in an Excited Impinging Jet Flow
Vejražka, Jiří ; Tihon, Jaroslav ; Cvetković, D.
The behavior of vortex structures is studied in an impinging jet of Reynolds number 10 000. The effect of the modulation of the nozzle exit velocity on the flow structure is studied by means of hot-wire anemometry. It is found that the velocity field can be modified by excitations of a wide range of frequencies. In most cases the excitation yields formation of large vortices, which provoke an unsteady flow separation at their impact onto the wall. The excitation at higher frequencies suppresses the roll-up of large eddies. The velocity fluctuations near the wall are then suppressed and the flow separation disappears. The effect is documented by phase averaging for the low nozzle-to-plate spacing. The time-averaged measurements show that the unsteady flow separation can be suppressed even for nozzle-to-plate spacing up to eight diameters.
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