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Analysis of the Velocity and Pressure Fields of the Liquid Using Curvilinear Coordinates
Stejskal, Jiří ; Kozubková, Milada (referee) ; Kučera,, Radek (referee) ; Veselý, Jindřich (referee) ; Pochylý, František (advisor)
This work introduces a new method of hydraulic design of a centrifugal pump impeller. This method is based on a geometrical approach employing curvilinear coordinates that are used to formulate both the axisymmetrical flow model in a meridional shape and the final model of flow in a blade cascade taking into account the full 3D shape of the impeller blade. The solution to this model then directly provides the guidelines for shaping the impeller blade in order to suppress the secondary flows, thus increasing the impeller efficiency, which is demonstrated on a real impeller design case. The partial differential equations describing the flow in the blade cascade are numerically solved piecewise on each particular stream surface, which leads to a significant reduction of computational time.
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Destratification of Reservoirs
Sluše, Jan ; Kozubková, Milada (referee) ; Šulc, Jan (referee) ; Pochylý, František (advisor)
This doctoral thesis is focused on design of new equipment for aeration of water surface with low depth of water column. Aeration is one of ecological preventive methods to prevent growth of cyanobacteria. Increase of dissolved oxygen content in water mass leads to support of the growth of organisms which are disadvantaged by impossibility of movement in water mass and thus also to support biodiversity. Given biodiversity has a positive effect on water quality because it avoids the outbreak of one species of aquatic organism, in particular of cyanobacteria. Designed aeration equipment uses membrane formed by hollow fibre to transport oxygen into the water. When aeration dissolution of oxygen occurs directly on the membrane surface which prevents air leak in the form of bubbles. This type of aeration has low operating costs and high efficiency of input of the oxygen into the water. Distribution in the aquatic environment is ensured by special boat. This boat is moving on the water surface and the technology is installed on the upper deck. The aeration is carried out by an aeration module situated in the water. The movement of the boat is partially ensured by autonomous control.
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Modeling of Liquid Film Instabilities with Subsequent Entrainment of Droplets
Knotek, Stanislav ; Kozubková, Milada (referee) ; Čermák, Libor (referee) ; Jícha, Miroslav (advisor)
This dissertation deals with instabilities of thin liquid films up to entrainment of drops. Four types of instabilities have been classified depending on the type of structure and process on the liquid film surface: two-dimensional slow waves, two-dimensional fast waves, three-dimensional waves, solitary waves and entrainment of drops from the film surface. This thesis analyzes the physical principles of instabilities and deals with the mathematical formulation of the problem. Shear and pressure forces acting on the surface of the liquid film are identified as the cause of instabilities. Mathematical models for predicting instabilities are demonstrated using approaches based on solving the Orr-Sommerfeld equation and the equations of motion in integral form. Models of shear and pressure forces acting on the surface of the film and selected models of film thickness are presented. The work is focused on the prediction of the initiation of two-dimensional waves using the integral approach. Shear stress and pressure forces acting on the liquid film surface have been modeled using the simulation of air flow over a solid surface. Finally, criteria for drop entrainment are presented with their dependence on air velocity and film thickness.
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Valveless Plunger Pump
Machů, Tomáš ; Kozubková, Milada (referee) ; Melichar, Jan (referee) ; Pochylý, František (advisor)
This thesis deals with valveless reciprocating pumps. Within the thesis several designs of pump geometry are demonstrated. Their parameters were obtained using computational fluid dynamics. Reciprocating piston movement was simulated by time dependent inlet boundary condition or by dynamic mesh. The individual variants were compared mainly from point of view of volumetric efficiency, which was the main evaluated parameter. Results of calculations are presented as dependencies of volumetric efficiency on frequency and amplitude of piston motion and on value of backpressure. Two variants of the prototype pump geometry were manufactured to experimentally validate parameters obtained from calculations. Volumetric efficiency together with hydraulic efficiency were evaluated from measured data.
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High Frequency Pulsation of Water Turbine in Operation
Kubálek, Jiří ; Kozubková, Milada (referee) ; Hružík, Lumír (referee) ; Haluza, Miloslav (advisor)
This thesis is concentrated on mathematical modeling of high frequency pulsations in pump turbines, which are the source of high-cycle continuous stress of the spiral casing cover, wicket gates and runner. There are proposed the solutions using the transfer matrix for the tube with a constant and conical cross-section. The paper compares variations of cylindrical and conical tubes, changes in boundary conditions. There are the models of PSPP Dlouhé Stráně made only of cylindrical tubes comparing to the model with cylindrical and conical tubes
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Numerical Simulation of Noise Generated by Shear Layer Instabilities
Šálený, Vratislav ; Kozubková, Milada (referee) ; Paur, František (referee) ; Tippner,, Jan (referee) ; Katolický, Jaroslav (advisor)
Predicting and inhibiting aerodynamically generated noise for fast moving vehicles such as cars, aircraft and trains is increasingly important. The tonal noise generated by the shear-layer instability of air flowing around the cavity opening is especially one of the most significant and most intense sources of aerodynamically generated noise. Computational aeroacoustics (CAA) based on the CFD simulations of compressible Navier-Stokes equations offers the most general approach to predicting those aerodynamically induced sounds. Aeroacoustics is practically always associated with turbulent flow and turbulence is the major challenge for CFD simulations. Four different turbulence modelling approaches are examined in this work. Three of them belong to the LES method category and one uses the URANS approach. Appropriate numerical discretization and iteration schemes have been identified for each of these approaches and implemented in the OpenFOAM open source CFD platform. The accuracy, computational performance and convergence reliability of those schemes have been subsequently studied during three-dimensional CFD simulations on a model of a suitable real object. The CFD simulation results are validated by a measurement. An organ pipe has been chosen as the object of this CAA research because it uses self-sustained oscillations, commonly referred as shear-layer (Rossiter) modes, as the source of its tone generation. The numerical simulation of the shear layer modes, respectively the noise generated by instability in the shear layer, is the subject of this work.
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Analysis of the Fluid Flow in Pipes Circular and Not Circular Cross-Section With Methods Using Distribution of the Vorticity Density
Soukup, Lubomír ; Kozubková, Milada (referee) ; Matas, Jakub (referee) ; Štigler, Jaroslav (advisor)
The doctoral thesis deals with the analysis of the flow in the circular and not circular cross-section pipes by methods using the distribution of the vorticity density. This analysis is particularly focused on the derivation of the new velocity profiles formulas using the above mentioned method. In this work is presented a historical overview of the derived velocity profiles. This overview of already derived velocity profiles will be a fundamental benchmark for newly derived velocity profiles. These new velocity profiles are derived for the circular and not circular cross-section pipes and the derivation is based on the analogy of electromagnetic induction by using Biot-Savart law. It is necessary to apply this analogy at first on solitary vortex filament. By taking this step is possible to get the value of the induced velocity from one solitary vortex filament. Subsequently it is possible to obtain the value of the induced velocity from the vorticity wall and afterwards from the vorticity density distribution over the cross section. This work contains also the results of the experimental measurements of the velocity profiles, and of the CFD simulations. Experimentally measured results are used besides other for the selecting of the most suitable CFD computational model. Selected CFD model will be subsequently declared as a reference model and the valid velocity profiles for this model will serve with the experimentally measured data as a benchmark for the newly derived velocity profiles.
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Disc friction loss in centrifugal pumps and hydraulic turbines
Zemanová, Lucie ; Kozubková, Milada (referee) ; Sedlář, Milan (referee) ; Rudolf, Pavel (advisor)
Dizertační práce je zaměřena na výzkum proudění v mezidiskových spárách hydraulických strojů s důrazem na čerpadla s nízkými specifickými otáčkami. Navzdory tomu, že tekutina v mezidiskových prostorách čerpadel zaujímá velmi malý objem, může výrazně ovlivnit proudění v celém stroji. To má následně vliv na provoz, charakteristiky a celkovou účinnost, zvlášť v případě čerpadel s nízkými specifickými otáčkami, protože stav proudění určuje vznikající diskové ztráty. Rovněž ovlivňuje rozložení tlaku a tím výslednou axiální sílu. Porozumění proudění v mezidiskových spárách je zatím omezené, současné poznatky vychází z teorie odvozené pro značně zjednodušený případ disku rotujícího v hladké válcové spáře. Použitelnost pro popis proudění ve skutečných hydraulických strojích je diskutabilní. Za účelem výzkumu proudění v reálném odstředivém čerpadle bylo navrženo a sestaveno experimentální zařízení umožňující pozorování proudění v zadní mezidiskové spáře pomocí optických metod, měření krouticího momentu a vznikající axiální síly. Také byla popsána metodika pro numerické simulace tohoto druhu proudění umožňující podchytit nestability a vírové struktury. Numerické simulace vhodně doplňují experimentální měření, rozšiřují rozmezí studovaných provozních podmínek a pomáhají popsat jevy, které by šlo měřením jen obtížně odhalit.
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Destratification of Reservoirs
Sluše, Jan ; Kozubková, Milada (referee) ; Šulc, Jan (referee) ; Pochylý, František (advisor)
This doctoral thesis is focused on design of new equipment for aeration of water surface with low depth of water column. Aeration is one of ecological preventive methods to prevent growth of cyanobacteria. Increase of dissolved oxygen content in water mass leads to support of the growth of organisms which are disadvantaged by impossibility of movement in water mass and thus also to support biodiversity. Given biodiversity has a positive effect on water quality because it avoids the outbreak of one species of aquatic organism, in particular of cyanobacteria. Designed aeration equipment uses membrane formed by hollow fibre to transport oxygen into the water. When aeration dissolution of oxygen occurs directly on the membrane surface which prevents air leak in the form of bubbles. This type of aeration has low operating costs and high efficiency of input of the oxygen into the water. Distribution in the aquatic environment is ensured by special boat. This boat is moving on the water surface and the technology is installed on the upper deck. The aeration is carried out by an aeration module situated in the water. The movement of the boat is partially ensured by autonomous control.
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