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Reduced order model of swirling flow
Urban, Ondřej ; Pochylý, František (referee) ; Rudolf, Pavel (advisor)
This thesis deals with the formulation and application of reduced order models based on extraction of dominant structures from a system utilizing the method of proper orthogonal decomposition. Time evolution of computed modes is described by a system of ordinary differential equations, which is gained by means of Galerkin projection of these modes onto the Navier-Stokes equations. This methodology was applied on two test cases Kármán vortex street and vortex rope. In both cases, a CFD simulation of one refference point was carried out and by utilizing gained modes, the corresponding reduced order models were formulated. Their results were assessed by comparing to the refference simulation.
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Water column separation under hydraulic turbine runner during unsteady operating regimes.
Vašek, Lubomír ; Rudolf, Pavel (referee) ; Habán, Vladimír (advisor)
In this diploma thesis called Water column separation under the hydraulic turbine runner during unsteady operating regimes are solved the pressure pulsations of the reverse water hamer. In the thesis is deduced a mathematical relationship of elaboration the numerice model which is based on equations of continuity and equations of forces equilibrium. Numerical model is created in MS Excel uses for computation the numerical method Lax-Wendrof that allows consideration of variable sound speed as function of static pressure and allows variable lenght step in computation domain. Reverse water hammer is in the thesis solved with consideration of rotating flow behind shut-off valve, where we expect forming of vortex rope. This situation can be applied on the closing water turbine which has vertex rope under turbine runner. Specifically for this thesis was carried out the experiment of the reverse water hammer. Constants going into numerical solution are optimalized with using experiment and pressure pulsation are compared between numerical solution and experiment.
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Study of vortical structures generated by a swirl generator
Kurková, Michaela ; Pochylý, František (referee) ; Urban, Ondřej (advisor)
This bachelor’s thesis deals with the study of vortical structures generated by a swirl generator. The theoretical part is focused on the description of experimental and numerical studies of the vortex rope phenomenon. This part also includes a brief overview of vortex identification methods. The second part is dedicated to the study of vortical structures captured by CFD simulations. The vortex identification methods are compared on an example of the vortex rope.
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Flow control in a hydraulic turbine draft tube
Litera, Jiří ; Štefan, David (referee) ; Rudolf, Pavel (advisor)
Hydraulic energy is one of the most important sources in the world for electricity production. Nowadays the trend is to limit the production of the electricity from fossil fuels and to protect the environment. The main idea is to use more renewable energy sources such as wind and solar energy. Unfortunately, these alternative sources are strongly dependent on current weather conditions, which causes the instability of the electrical grid. Luckily pumped storage and hydraulic power plants provide the solution. However, it requires an extension of the operating range of the hydraulic machines. For that reason, the water turbines now operate over and extended range of regimes, that can be quite far from the best efficiency point. Hence two types of unstable two-phase flows in the Francis turbine draft tube occur: part load overload. This diploma’s thesis is focused on the Francis turbine operating at the part load. During part load conditions the helical vortex rope is being developed in the draft tube, it causes pressure pulsation and it can lead to the hydro-acoustic resonance, which damages the elements of the power plant. The aim is to eliminate the pulsation by jet control of the swirling flow in the draft tube. In the diploma’s thesis, various approaches to jet control of the flow in conical diffuser are tested using the computational fluid dynamics.
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Draft tube role in hydraulic turbine performance
Havlát, Pavel ; Himr, Daniel (referee) ; Rudolf, Pavel (advisor)
This bachelor’s thesis deals with the problems of draft tube. It contains basic description of draft tubes, their division and possibilities of their utilizations. Further, this thesis focuses on description of draft tubes, their efficiency, losses and ways to eliminate these losses. One part of this work also mentions basic relationships required for computing length of draft tube, velocity of the fluid in the draft tube and others.
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Vortex rope for overload operation of Francis turbine
Kozák, Jiří ; Štefan, David (referee) ; Rudolf, Pavel (advisor)
This master's thesis deals with CFD simulation of vortex rope in the elbow draft tube for overload operation of Francis turbine. The main objective of the thesis is to compare results of the CFD simulations of the original elbow draft tube with a derived straight cone draft tube considering volume and the shape of the cavitation region and dynamic flow characteristic. Results of the 3D simulations are also compared with axi-symmetric simulations, which reduce demands for computing time and power.
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Vortex breakdown
Lunda, Filip ; Rudolf, Pavel (referee) ; Urban, Ondřej (advisor)
The bachelor thesis deals with the vortex breakdown phenomenon. The first part focuses on a description of the vortex breakdown and its own characteristics. The next part deals with the theoretical description. After that, an enumaration of experimental devices used for observation of vortex breakdown follows. The last chapter contains information about control of this phenomenon.
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CFD simulation of vortex structure in the Francis turbine draft tube at part load operating point - comparison with measurements
Neděla, Jiří ; Urban, Ondřej (referee) ; Štefan, David (advisor)
This master's thesis deals with simulation of vortex structure which is created in the draft tube of Francis turbine, at part load flow conditions. The main objective is to get the most accurate results from the calculations, using the student license of Ansys Fluent 19.1. The results from the calculations are compared with the experiment under the Francis-99 project. Mainlly in terms of dynamic properties of vortex rope – aplitude and frequency of pressure pulsations. Additionaly the time-averaged velocity profiles are compared. I used the test-case provided by NTNU – Norwegian University of Science and Technology under the Francis-99 workshop series.
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Computer graphics flow visualization methods
Častulíková, Veronika ; Štefan, David (referee) ; Urban, Ondřej (advisor)
Flow visualization is one of the important topics in the scientific visualization, which is a subject of ongoing research. Data obtained by numerical simulations are further analysed to gain a better understanding of fluid flow. With the rapid development of computational simulations, demand for more advanced visualization methods has grown. Basic overview and a detailed description of the fluid flow visualization techniques is introduced in the bachelor thesis. Afterwards, the techniques are applied on data obtained by CFD simulation of a vortex rope in the draft tube swirl generator.
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