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Eigenmodes of the swirling flow
Jízdný, Martin ; Pochylý, František (referee) ; Rudolf, Pavel (advisor)
This thesis deals with study of dynamics of the swirling flow. The swirling flow occurs frequently in hydraulic machinery (e.g., vortex rope in draft tube of the hydraulic turbine) and often influences operation of these machines. For this reason, sufficient knowledge regarding this characteristic flow is necessary for subsequent improvement of hydraulic machines. The theoretical part of this thesis contains description of flow instabilities and their manifestations, notably Kármán vortex street and vortex rope. In the next part, two methods are applied to these two transient flows in order to identify their specific dynamic properties. The first method, Fourier transform, enables to find frequencies of transient flow. The second method, proper orthogonal decomposition (POD), enables to identify planar or spatial eigenmodes of a specific swirling flow. Proper orthogonal decomposition is used in this thesis to identify planar eigenmodes of Kármán vortex street and spatial eigenmodes of vortex rope.
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From tornado to hydraulic turbine
Jízdný, Martin ; Rinka, Lukáš (referee) ; Rudolf, Pavel (advisor)
This bachelor thesis deals with vortex motion and contains two main parts. The first part refers to the principles of creation and evolution of vortex motion in nature and in technological applications. In both of these fields it is possible to find positive and negative impacts of vortex motion which influence the world significantly. The second part of this bachelor thesis refers to an experiment which main goal was to verify some selected qualitites of vortex motion and to determine hypothesis based on measurements. The final part of the experiment deals with the different methods of making vortex motion visible in laboratory conditions.
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Multiphase CFD simulation of spiral vortex in vaneless swirl generator
Zatloukal, Filip ; Burda, Radim (referee) ; Štefan, David (advisor)
This thesis deals with multiphase CFD simulation of spiral vortex in bladeless swirl generator. Spiral vortex formed in the draft tube of hydraulic turbine is called “vortex rope”. Vortex rope is formed when the turbine is forced to operate in off-design conditions. Assessment of swirl generators used for the study of vortex ropes is presented. The multiphase CFD simulations are carried out for the bladeless swirl generator with use of Reynolds stress turbulence model in ANSYS Fluent software. The results from calculations are compared with available experimental data previously measured on this particular swirl generator. The main focus is on detailed analysis of velocity field in the diffusor part of the generator where the vortex appears. Experimentally estimated swirl number is compared with the one evaluated from simulation. The swirl number is also monitored along the length of diffuser and downstream. Finally, the synchronous and asynchronous pressure pulsations are studies by means of Fast Fourier Transformation.
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Reduced order model of the swirling flow
Urban, Ondřej ; SUSAN-RESIGA, Romeo Florin (referee) ; Uruba, Václav (referee) ; Rudolf, Pavel (advisor)
Tato dizertační práce je zaměřená na studium vírového copu. Za tímto účelem byl navržen nový vírový generátor umožňující regulaci intenzity zavíření. Chování vírového copu bylo studováno jak numericky, tak experimentálně. Byly použity numerické simulace zachycující i část energetické kaskády turbulentního proudění, dále byly navrženy metody vizualizace dat založené na objemovém renderování a byla testována různá vírová kritéria. Také bylo studováno několik metod dekompozice proudových polí. Nakonec byly navrženy metody pro extrakci kvaziperiodických módů. S využitím těchto metod byl sestaven redukovaný model pro daný rozsah provozních bodů.
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Multiphase CFD simulation of spiral vortex in vaneless swirl generator
Zatloukal, Filip ; Burda, Radim (referee) ; Štefan, David (advisor)
This thesis deals with multiphase CFD simulation of spiral vortex in bladeless swirl generator. Spiral vortex formed in the draft tube of hydraulic turbine is called “vortex rope”. Vortex rope is formed when the turbine is forced to operate in off-design conditions. Assessment of swirl generators used for the study of vortex ropes is presented. The multiphase CFD simulations are carried out for the bladeless swirl generator with use of Reynolds stress turbulence model in ANSYS Fluent software. The results from calculations are compared with available experimental data previously measured on this particular swirl generator. The main focus is on detailed analysis of velocity field in the diffusor part of the generator where the vortex appears. Experimentally estimated swirl number is compared with the one evaluated from simulation. The swirl number is also monitored along the length of diffuser and downstream. Finally, the synchronous and asynchronous pressure pulsations are studies by means of Fast Fourier Transformation.
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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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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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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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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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