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Study of the Dissipation in Spiraling Vortical Structures
Štefan, David ; Drábková, Sylva (referee) ; Koutník,, Jiří (referee) ; Skoták, Aleš (referee) ; Rudolf, Pavel (advisor)
This work deals with study of swirling flows where the spiral vortical structure appears. The main relation is to flow seen in the draft tube cone of hydraulic turbines operated out of the design point (i.e. best efficiency point). In this cases large coherent vortex structure (vortex rope) appears and consequently high pressure pulsations are propagated to the whole machine system leading to possible restriction of turbine operation. This flow features are consequence of flow instability called vortex breakdown in case of Francis turbine operated at part load (flow rate lower than optimal one). The present study is carried out using simplified device of swirl generator in order to access similar flow conditions as can be found in real hydraulic turbines. Both the dynamic and dissipation effect of spiral vortex breakdown are investigated. The first part of thesis deals with spiral form of vortex breakdown. The experimentally measured velocity profiles (LDA) and wall static pressures are correlated with numerical simulations carried out using open-source CFD package OpenFOAM 2.2.2. The high speed camera recording of cavitating vortex core is used to obtain image ensemble for further post-processing. The dissipation effect of spiral vortex structure is in detail discussed based on computed flow fields. The second part of thesis is dedicated to the application of POD decomposition to the study of spatio-temporal features of spiral vortex dynamics. Firstly the POD is applied to the both the experimentally obtained image ensemble of cavitating vortex and numerically computed static pressure fields. Secondly the comprehensive analysis of spiral vortex mitigation effect by the axial water jet is analyzed. The collaborative study employing the swirl generator apparatus designed by the researchers from Politehnica University of Timisoara in Romania is performed and changes in spatio-temporal vortex dynamic are studied. In this study the numerical data (in a form of three-dimensional pressure and velocity fields) are obtained using commercial CFD software ANSYS Fluent R14.
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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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Contradictions analysis of small water power Ostravice.
Kupčík, Roman ; Skoták, Aleš (referee) ; Haluza, Miloslav (advisor)
The main subject of the diploma thesis „Contradiction analysis of small water power Ostravice“ is solution of reduced output of small water power plant on the river Ostravice near the town Vratimov. Power plant equippment is axial flow Kaplans turbine RA – 3,5 – 0 1000 with runner diametr 1000 mm. Low output is caused by draft tube. New draft tube is designed in this masters thesis. For hydraulic layout was used CFD software Fluent. The aim of this work is finding of optimal shape which leads to increasing of power from current 30 kW to projected 55 kW.
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Swirl turbine design
Šperka, Oldřich ; Skoták, Aleš (referee) ; Haluza, Miloslav (advisor)
The purpose of this diploma work is to predict the action of the swirl turbine in a siphonal configuration using the potential energy provided by the river Úpa near the city Jaroměř. The hydraulic predictions of the turbine impellor were based on calculation made using the CFD program Fluent. The measurement of the draft tube and the strength calculations of the turbine blade and spindle are based upon the theories, experiments and finally on the knowledge gained from the test models constructed. The results of this project can be used when considering the viability of a small hydraulic power plant.
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Numerical simulation of rotor-stator interaction (RSI) of Francis turbine
Machoň, Matěj ; Skoták, Aleš (referee) ; Štefan, David (advisor)
The master's thesis deals with the numerical simulation of rotor-stator interaction (RSI) of Francis turbine. In the selected operating point of the machine, the pressure amplitudes belonging to RSI frequencies are evaluated in various pressure sensors and compared with available experimental data. Various simplifications of the simulation, namely using Transient Blade Row Modelling, are done and their impact on results is investigated. Lastly the modal analysis with acoustics elements present is performed to obtain the eigenfrequencies and mode shapes of the runner submerged into water to be able to conclude, if the resonance occured.
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The influence of number and position of stay vanes on characteristic of Francis turbine
Mraček, Pavel ; Skoták, Aleš (referee) ; Haluza, Miloslav (advisor)
The thesis deals with the influence of the number and position of stay vanes on the characteristic of a Francis turbine. The main objective is to find the most hydraulically advantageous configuration by CFD simulations. It was important for this work to use comparable methods, in particular the same turbulence model and computational grid. The output of the thesis is a comparison of hydraulic losses for different configurations of the position of guide vanes and number of stay vanes.
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Flow structure and energy transformation in an elbow draft tube
Štefan, David ; Skoták, Aleš (referee) ; Rudolf, Pavel (advisor)
Draft tube is very important part of hydraulic turbines. Only optimum work together with turbine can bring highest performance of this machine set. Hence it is necessary to deal with character of flow in the draft tube for different operating conditions. Efficiency of the draft tube depends on many phenomena of flow. Observing these phenomena and finding their relation with energetic transformation in the draft tube is a suitable tool to judge quality of draft tube performance. Incorrect design of the draft tube can sometimes cause lower efficiency of whole machine set. The goal of this thesis is finding the main reasons causing draft tube efficiency drop for given operating conditions.
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The influence of number and position of stay vanes on characteristic of Francis turbine
Mraček, Pavel ; Skoták, Aleš (referee) ; Haluza, Miloslav (advisor)
The thesis deals with the influence of the number and position of stay vanes on the characteristic of a Francis turbine. The main objective is to find the most hydraulically advantageous configuration by CFD simulations. It was important for this work to use comparable methods, in particular the same turbulence model and computational grid. The output of the thesis is a comparison of hydraulic losses for different configurations of the position of guide vanes and number of stay vanes.
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Numerical simulation of rotor-stator interaction (RSI) of Francis turbine
Machoň, Matěj ; Skoták, Aleš (referee) ; Štefan, David (advisor)
The master's thesis deals with the numerical simulation of rotor-stator interaction (RSI) of Francis turbine. In the selected operating point of the machine, the pressure amplitudes belonging to RSI frequencies are evaluated in various pressure sensors and compared with available experimental data. Various simplifications of the simulation, namely using Transient Blade Row Modelling, are done and their impact on results is investigated. Lastly the modal analysis with acoustics elements present is performed to obtain the eigenfrequencies and mode shapes of the runner submerged into water to be able to conclude, if the resonance occured.
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