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Utilization of hydrodynamic cavitation for water treatment
Balko, Marek ; Kozák, Jiří (referee) ; Rudolf, Pavel (advisor)
This bachelor thesis deals with the observation of features of cavitation with emphasis on the hydrodynamical cavitation and its use for eliminating unwanted and badly degradable compounds from water. Thanks to high temperature and pressures that are present at a colapse of cavitation bubbles the water decomposes into highly reactive hydroxile radicals which are able to decompose even. This effect can furthermore be strenghtened by the use of advanced oxidation processes – AOP. The experimental part of thesis is dedicated to examining a ability of hydrodynamical cavitation degrade particular chemical substance from water, namely estrogen.
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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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Monitoring of hydraulic machines using acoustic emissions
Závorka, Dalibor ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
The goal of this diploma thesis is to clarify possibilities of usage of acoustic emission as a hydraulic machinery diagnostics tool. Especially for exposing presence of ruptures or cracks in the parts of machine, assuming changes in acoustic exposure of the part during operation. This clarification is based on series of simple measured experiments, which consist of monitoring the bolt placed in fluid stream inside of a pipe. This bolt was preloaded against inner wall of pipe by appropriate tightening torque. This preload is supposed to simulate effects of the size of rupture. High preload simulates small rupture or none in object and respectively small preload is supposed to simulate big rupture. A group of pressure sensors and accelerometers measures experiments and their evaluations are processed by script created in software MATLAB. Outputs of this script are charts with effective values of respective sensors from the entire record split into individual frequency spectrums. These charts compare spectrums of each configuration to judge effects of parameters changes.
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Influence of fractal geometry on turbulent flow
Hochman, Ondřej ; Štefan, David (referee) ; Rudolf, Pavel (advisor)
The master’s thesis deals with computational fluid dynamics (CFD) of two orifices, that have different shapes of holes but similar cross-sectional flow areas. The first of them is orifice with circular-shaped hole, which is used for maintenance free measurement of flow. The second one is orifice with fractal-shaped hole, inspired by von Koch snow-flake. This thesis follows bachelor thesis, in which was experimentally examined, that fractal-shaped orifices have better hydraulic properties (hydraulic losses and lower pressure pulsations) than circle-shaped one. The main target is to confirm this conclusion based on experiment, this time using CFD with various types of turbulence modelling ap-proaches. Both single phase (cavitation free) and multiphase numerical simulations were realized. Each model was compared from perspective of hydraulic and dynamic charac-teristics.
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Cavitating jet
Kotoulová, Helena ; Kozák, Jiří (referee) ; Rudolf, Pavel (advisor)
Předložená diplomová práce se zabývá kavitujícím paprskem a je rozdělena do tří hlavních částí. Teoretická část popisuje základní principy kavitace a její negativní účinky na povrch obtékaných těles (např. hydraulických strojů). Rozsáhlá kapitola je také věnována popisu samotného kavitujícího paprsku včetně mechanismů jeho vzniku, růstu a kolapsu. Další podkapitola je zaměřena na modely kavitační eroze, které mají velký význam pro predikci kavitační eroze ve fázi výpočtové simulace. V experimentální části je popsáno testování vzorku mědi inspirované normou ASTM G134 a následné vytvoření grafů kumulativního hmotnostního úbytku a rychlosti úbytku hmotnosti. Dále byla také provedena vizualizace pomocí vysokorychlostní kamery, aby bylo možné podrobně prozkoumat dynamické chování kavitujícího paprsku. Poslední část je zaměřena na numerické simulace pomocí výpočtového modelování proudění, tzv. Computational Fluid Dynamics (CFD), a na predikci kavitační eroze. Z důvodu optimalizace úlohy bylo provedeno více výpočtů na různých typech sítí s různými modely turbulence. Následně byly výsledky ze simulací vyhodnoceny a společně s výsledky z experimentu byly použity pro predikci kavitační eroze.
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Analysis of measured signals from cavitation experiments
Asszonyi, Ondřej ; Habán, Vladimír (referee) ; Rudolf, Pavel (advisor)
This thesis focuses on problem with detection of cavitation in hydraulic systems and devices. Thesis works with data from cavitation tunnel experiment, where cavitation appeared on blade. It founds out if time records and their frequency spectrum is dependent on operating conditions. Data are examined by various statistic methods. All of that is then used in method called neural network.
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Hydraulic characteristics of the cavitation nozzles
Gríger, Milan ; Habán, Vladimír (referee) ; Rudolf, Pavel (advisor)
The main goal of this thesis is the examination of hydraulic characteristics for different cavity nozzles, influence of liquid rotation and visualization of cavitating flow. Thesis is divided into two parts, theoretical and practical. Theoretical part deals with the description of cavity - creation, development and its extinction. This part also contains description of vortex flow and basic vertex models. Practical part compares nozzles performance experimentally. The aim of experiment was to measure hydraulic characteristics and their comparison. Jet performance was judged using visualizations and measured data was processed in Microsoft Excel and Parametr.
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