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Microfluidic devices
Stehlík, Martin ; Sluše, Jan (referee) ; Rudolf, Pavel (advisor)
The bachelor's thesis deals with the phenomenon of mixing fluid in an equipment with micro scale and its production. The first part is dedicated to describe Reynolds, Peclet and Strouhal number. The second part describes micromixers and their distribution. The final part deal´s with specific examples of manufacturing microfluidc devices.
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Influence of the Francis turbine stay vane trailing edge shape on generation of Karman vortex street
Novotný, Vojtěch ; Skoták, Aleš (referee) ; Rudolf, Pavel (advisor)
In the flow past bluff bodies for a certain range of velocity a periodical vortex shedding emerges which is known as von Kármán vortex street. This phenomenon causes the periodical alteration of pressure field which affects the body. Should the vortex shedding frequency be similar to the body natural frequency, the amplitude of vibration significantly increases which can lead to fatigue cracking. In the case of water turbines, this phenomenon often affects the stay vanes. Both the vortex shedding frequency and the lift force amplitude can be influenced by the modification of the trailing edge geometry. The aim of this thesis is to use CFD computation in order to find the optimal geometry of the stay vane trailing edge for the specific Francis turbine unit.
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Wind loads of building structures
Štěrba, Martin ; Kala, Jiří (referee) ; Hradil, Petr (advisor)
The bachelor thesis deals with the analysis of the effects of wind load on building structures. In the context of the work is solved the numerical modeling of flow around the solid cylindrical bodies at high Reynolds numbers. To the simulations has been used computational software ANSYS CFX. The outputs of the work are the values of Strouhal numbers and the values of drag and lift coefficient depending on the Reynolds number.
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Wind load on cooling tower
Ehrlich, Tomáš ; Kala, Jiří (referee) ; Nevařil, Aleš (advisor)
Thesis is concerned with modeling fluid dynamics and computing wind load on thin-walled structure of cooling tower. Two models for computational fluid dynamics are presented – one with singleton cooling tower and second with group of four cooling tower. Thesis includes also a structural model of cooling tower and methodology of wind load transfer is presented.
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Laboratory Model of the Vortex Speed Indicator
Kazda, Ondřej ; Kolka, Zdeněk (referee) ; Biolková, Viera (advisor)
This work is concerned with posibility of measuring a wind flow by Von Karman vortex sheed structure. The bluff body is situated in the way of air flow propagation and consequentally vortexes will be appeared. Important part of speedmeter design is measurment chamber must allow to vortex sheed propagation. The transient and the reciever are situated vertically to propagation of flow.The Ultrasonic carrier is transmitted and modulated by freqency of vortex sheeding in measurment chamber.Demodulator uses PLL to “focusing“ detection of the ultrasonic beam. This can be indicated like lock and unlock phase loop. From known value of sheed frequency can be directly calculated speed of flow.
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Effect of Cylinder Roughness on Strouhal Number
Yanovych, Vitalii ; Duda, D. ; Uruba, Václav ; Procházka, Pavel P. ; Antoš, Pavel
The main goal of this paper is to establish a better understanding of the relationship between a Strouhal number and surface roughness. Hot-wire anemometry was used to evaluations the characteristics of turbulent flow behind circular cylinders with different relative roughness 0% (smooth surface) 0.83%, 1.67%, 3.33%, and 6.67%. At the experimental investigation, the Reynolds number based on the cylinder diameter was 5 × 103 < Red < 2 × 104. The obtained data showed that the Strouhal number decreased with increasing roughness. While, the dissipation rate decreases, and the value of the Kolmogorov and Taylor microscales increases. Also, spectral analysis of streamwise velocity fluctuations allowed us to estimate the location of the vortex-shedding frequency which at growing roughness tends to reduce.
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On Harmonic Content of the Wake Behind a Circular Cylinder
Uruba, Václav ; Procházka, Pavel P.
The wake behind cylinder of circular cross-section is subjected to detailed analysis from the point of view harmonic content. The basic, fundamental frequency could be linked to well-known Bénard-von Kámán vortex street, it is called Strouhal frequency very often. However higher harmonics of 2nd and 3rd order have been detected, as well as important inharmonic partials. The topologies of the velocity flow-field corresponding to the harmonic is to be shown.
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Investigation of Strouhal number of ice-accreted bridge cables at moderate flow turbulence
Górski, P. ; Tatara, M. ; Pospíšil, Stanislav ; Kuznetsov, Sergeii
This paper is concerned with the investigation of the Strouhal number (St) for a stationary iced cable model of cable-supported bridges using wind tunnel tests with respect to three principal angles of wind attack. The investigations were carried out in the Climatic Wind Tunnel Laboratory of the Czech Academy of Sciences in Telč. The St values were determined at the flow turbulence intensity of the order of 12%, within the range of the Reynolds number from 2.4·10^4 to 12.9·10^4, based on the dominant vortex shedding frequencies measured in the wake of the model. The obtained experimental St values of the iced cable of a cable-supported bridge will allow to determine the critical wind velocity as well as will be helpful for prediction of the cable response due to the vortex excitation phenomenon at moderate flow turbulence condition.
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Influence of the Francis turbine stay vane trailing edge shape on generation of Karman vortex street
Novotný, Vojtěch ; Skoták, Aleš (referee) ; Rudolf, Pavel (advisor)
In the flow past bluff bodies for a certain range of velocity a periodical vortex shedding emerges which is known as von Kármán vortex street. This phenomenon causes the periodical alteration of pressure field which affects the body. Should the vortex shedding frequency be similar to the body natural frequency, the amplitude of vibration significantly increases which can lead to fatigue cracking. In the case of water turbines, this phenomenon often affects the stay vanes. Both the vortex shedding frequency and the lift force amplitude can be influenced by the modification of the trailing edge geometry. The aim of this thesis is to use CFD computation in order to find the optimal geometry of the stay vane trailing edge for the specific Francis turbine unit.
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