In the flow past bluff bodies for a certain range of velocity a periodical vortex shedding emerges which is known as von Kármán vortex street. This phenomenon causes the periodical alteration of pressure field which affects the body. Should the vortex shedding frequency be similar to the body natural frequency, the amplitude of vibration significantly increases which can lead to fatigue cracking. In the case of water turbines, this phenomenon often affects the stay vanes. Both the vortex shedding frequency and the lift force amplitude can be influenced by the modification of the trailing edge geometry. The aim of this thesis is to use CFD computation in order to find the optimal geometry of the stay vane trailing edge for the specific Francis turbine unit.

In this thesis, a miniaturized energy harvester system is developed. The energy harvester converts fluid kinetic energy into electrical energy without using any rotating components. The working principle of the energy harvester is based on the so called vortex-induced vibration. Such systems have the potential to provide energy for wireless sensor networks in the field of inline measurements for gas, oil or water transportation systems. The theoretical background of the vortex-induced vibration (VIV) is studied. Based on the studies, a fluid-structure interaction simulation is carried out to optimize the structure of the energy harvester. As result, the conversion efficiency is significantly improved, which is experimentally confirmed. A series of demonstrators are manufactured according to the simulation and optimization results. It is tested on a self-constructed test bench. To further improve the performance, an electromagnetic generator is proposed, and therefore, a multimethod demonstrator realized. The demonstrators are working in air flow already at a velocity of 2 m/s, and reach the maximum efficiency at 3.6 m/s. This performance ranks among the best published results and is discussed in detail. / In der vorliegenden Arbeit wird ein miniaturisiertes Energiegewinnungssystem entwickelt, das unter Verzicht auf rotierende Komponenten kinetische Strömungsenergie in elektrische Energie umwandelt. Die Funktion dieses Wandlers basiert auf der sogenannten wirbelinduzierten Vibration. Derartige Systeme besitzen unter anderem das Potenzial, drahtlose Sensornetzwerke zur Erfassung von Messdaten in Gas-, Öl- oder Wassertransportsystemen mit Energie zu versorgen zu können. In der Arbeit wird der theoretische Hintergrund der wirbelinduzierten Vibration untersucht und darauf basierend werden Fluid-Struktur-Wechselwirkungssimulationen zur Strukturoptimierung durchgeführt in deren Ergebnis eine theoretische Verbesserung der Effizienz des Wandlers um ein Mehrfaches erreicht wird, die auch praktisch bestätigt wird. Unter Berücksichtigung der Simulations- und Optimierungsergebnisse wurden eine Reihe von Demonstratoren gefertigt, die auf einem selbst konstruierten Prüfstand getestet wurden. Zur weiteren Erhöhung der Leistungsfähigkeit des Wandlers wird ein zusätzlicher elektromagnetischer Generator vorgeschlagen und damit ein Multi-Methoden-Demonstrator technisch realisiert. Die Demonstratoren arbeiten in strömender Luft bereits bei Geschwindigkeiten von 2 m/s und erreichen bei 3,6 m/s ihre maximale Effizienz. Die erreichten Ergebnisse ordnen sich im Vergleich mit denen aus entsprechenden Publikationen vorn ein und werden ausführlich diskutiert.

The aim of the dissertation thesis is the control of the tube bundle on the cyclic fatigue caused by the flow past tube bundle. Fatigue due to flow is caused by flow-induced vibrations. Examined vibrations are caused by the mutual interaction of two phases (solid and liquid). The present work is focused mainly on the interaction of tube bundles with fluid. The current level of knowledge in this field allows to predict mainly static respectively quazi-static loading. These predictions are based on methods of comparing key vibration variables such as frequencies, amplitudes or speeds (see TEMA [1]). In this way, it is possible to determine quickly and relatively precisely the occurrence of a vibrational phenomenon, but it is not possible to quantitatively assess the effect of these vibrations on the damage of to the tube beam and to predict its lifespan, which would require the determination of the temperature field and the distribution of forces from the fluid on the beam. The aim of the work is to evaluate the-state-of-the-art, to perform a numerical simulation of the flow of fluids in the area of shell side under the inlet nozzle. Current methods of numerical analyses very well solve this problem, but at the expense of computing time, devices and expensive licences. The benefit of this work is the use of user-defined function (UDF) as a method for simulating interaction with fluid and structure in ANSYS Fluent software. This work places great emphasis on using the current state of knowledge for verifying and validation. Verifying and validation of results include, for example, experimentally measured Reynolds and Strouhal numbers, the drag coefficients and for example magnitude of pressure coefficient around the tube. At the same time, it uses the finite element method as a tool for the stress-strain calculation of a key part on tube such as a pipe-tube joint. Another benefit of this work is the extension of the graphical design of heat exchanger according to Poddar and Polley by vibration damages control according to the method described in TEMA [1]. In this section, the author points out the enormous influence of flow velocity on both the tube side and the shell side for design of the heat exchanger to ensure faultless operation. As an etalon of damage, the author chose a heat exchanger designated 104 from the Heat Exchanger Tube Vibration Data Bank [3]. With this heat exchanger, vibrational damage has been proven to be due to cutting of the tubes over the baffles. The last part outlines the possibilities and limits of further work.