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Energie rázové vlny vzniklé při růstu bubliny ve vodě a generované při jejím kolapsu
Müller, M. ; Maršík, František
The Kirkwood – Brinkley theory of propagation of spherical shock wave is used to evaluate the amount of the energy transformed into the shock wave generated during the rise of cavitation bubble generated by Nd-Yag laser. The energy was according to the theory calculated from known shock wave velocity, shock wave position and shock wave pressure-time profile at the defined position. Method of characteristic in the Kirkwood – Bethe modification was used for the calculation of the shock wave pressure time profile. The initial conditions for the calculation of the outgoing characteristic were obtained by solving Rayleigh-Plesset equation in Gilmore modification.
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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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Pasivní a aktivní metody řízení mezní vrstvy
Matějka, Milan ; Popelka, Lukáš
The paper deals with influence of the passive and active method of control on the flow field. It is well known fact that boundary layer separation has a fundamental effect on aircraft airfoil performance, compressors and turbines performance and other bodies, subject to study of internal and external aerodynamics. By the boundary layer control, it is possible to obtain both operational economy and extension of efficient operational region. Traditional methods of active boundary layer control are very complex and their application needs complex facilities. Modern methods based on the control by synthetic jets or plasma actuator are simpler, but their design has to be carried out at rather well experience and detailed knowledge about boundary layer and its interaction with the actuator.
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Study of velocity field in crossroads areas
Kellnerová, Radka ; Jaňour, Zbyněk
The aim of this project is to study the influence of boundary conditions on contaminant spreading in a urban area model. The urban area model was composed of simple elements shapes of crossroads: X-shaped, T-shaped and skew intersection. The project at the beginning - by now only results for T-shaped crossroads are available. The experiment took place in an environmental aerodynamics tunnel IT AS CR in Nový Knín. First results show accumulation of high values of Reynolds stress above the area of crossroads center, whereas the velocity field is weaker when compared with more remote area. In specific distance from the intersection the recirculating zone appears. With increasing distance from intersection the center of zone moves counter main flow and up.
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Proudění a rozptyl zněčištění v idealizované městské zástavbě
Šeděnková, Hana ; Jaňour, Zbyněk
The aim of the experiment was a measurement of the flow in the urban canopy layer - the portion of boundary layer of atmosphere between the roof tops and the ground. The work took place in the boundary layer wind tunnel. The Laser Doppler Anemometry was used as a flow measurement technique. The simplified model of the urban build-area (regularly placed cubes on the ground) was put into the tunnel. The big influence of the model on the flow was found.
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