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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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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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Model order reduction technique for large scale flow computations
Isoz, Martin
Current progress in numerical methods and available computational power combined with industrial needs promote the development of more and more complex models. However, such models are, due to their complexity, expensive from the point of view of the data storage and the time necessary for their evaluation. The model order reduction (MOR) seeks to reduce the computational complexity of large scale models. We present an application of MOR to the problems originating in the finite volume (FV) discretization of incompressible Navier-Stokes equations. Our approach to MOR is based on the proper orthogonal decomposition (POD)\nwith Galerkin projection. Moreover, the problems arising from the nonlinearities present in the original model are adressed within the framework of the discrete empirical interpolation method (DEIM). We provide a link between the POD-DEIM based MOR and OpenFOAM, which is an open-source CFD toolbox capable of solving even industrial scale problems. The availability of a link between OpenFOAM and POD-DEIM based MOR enables a direct order reduction for large scale systems originating in the industrial practice.
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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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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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Wavelet and POD Analysis of Turbulent Flow Within Street Canyon
Kellnerová, Radka ; Kukačka, Libor ; Uruba, Václav ; Antoš, Pavel ; Odin, J. ; Jaňour, Zbyněk
Wavelet analysis of flow inside the street canyon is applied on highrepetition PIV and high-frequency hot wire data. Experiment is performed in windchannel with floor covered by series of street canyons.The passage of sweep and ejection events is detected as being long-term signature in lower frequencies. The passage of vortex is recognizable as circular patterns in higher frequencies on Wavelet spectrum.When using velocity vectors as input data, proper orthogonal decomposition (POD) reveals the most dominant modes in terms of turbulent kinetic energy.
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