Os resultados de uma simulação numérica são apresentados para amplitudes de vibração induzidas por um escoamento transversal num feixe tubular no regime de instabilidade fluidelástica.O feixe tubular considerado tem geometria e características iguais às de uma instalação equivalente descrita na literatura, para a qual estão disponíveis as medições experimentais das amplitudes de vibração no regime de instabilidade elástica.O arranjo tipo triângulo rodado tem uma relação passo/diâmetro de 1,375 e consiste de um tubo móvel cercado por 134 tubos rígidos.A simulação numérica foi efetuada através de um software comercial de CFD (Computational Fluid dynamics).Para a região em torno de cada tubo foi considerada uma malha com dimensões do elemento crescendo geometricamente na direção normal ao tubo com fator de crescimento 1,13 , sendo a dimensão do elemento adjacente ao tubo igual a 0,1% do diâmetro externo do tubo.Na simulação numérica o escoamento foi considerado incompressível, monofásico, turbulento e bidimensional. Os dados do escoamento foram considerados idênticos aos das experiências da instalação descrita na literatura.Os resultados obtidos para as amplitudes pela simulação numérica são comparados com os resultados obtidos experimentalmente na instalação acima citada.Os desvios da maioria dos valores calculados em relação aos valores experimentais estão numa faixa aceitável. Isto mostra que existe a possibilidade de utilização, num futuro próximo, de CFD para análise deste tipo de problemas. / Results from a numerical simulation are reported for amplitudes of cross-flow induced vibrations at the fluid elastic instability regime in a tube bank. The tube bank has identical geometry and characteristics as for an experimental facility described in the literature, for which there are experimental measurements of the amplitudes of vibrations at the fluid elastic instability regime.The rotated triangular array has a pitch ratio of 1.375 and consists of 1 movable tube surrounded by 134 rigid tubes. The numerical simulations were accomplished with a commercial CFD (Computational Fluid Dynamics) software. For the region around each tube, a mesh with elements dimensions growing geometrically normal to the tube was considered, with growing factor 1.13, and the dimension for the element adjacent to the tube wall was set to 0.1% of the tube external diameter. The flow was considered incompressible, monophasic, turbulent and two-dimensional for the numerical simulation. The flow data considered were the same as for the experiments at the facility. The results presented in this paper for the amplitudes obtained by numerical simulation are compared with the experimental results obtained in the above mentioned experimental facility.The differences between the calculated values and the experimental values are acceptable. This show that in the near future there is the possibility to use CFD for these kind of problems.

A vibração induzida por escoamento é parte intrínseca do transporte de fluidos. Por exemplo, na indústria de petróleo e gás esse fenômeno pode ser encontrado em tubulações, tanto no setor upstream, quando downstream. Essas vibrações são produto das forças geradas pelo escoamento e, portanto, carregam informações sobre sua fenomenologia. No caso de escoamento bifásico em tubo, resultados experimentais indicam forte influência da velocidade da mistura, fração de vazio e padrão de escoamento no comportamento dinâmico da estrutura. Contudo, pouco foi feito na tentativa de obter informações do escoamento a partir da reposta estrutural. Assim, o objetivo do presente estudo é desenvolver métodos para a previsão dos parâmetros do escoamento baseados na resposta de um tubo submetido a escoamento bifásico. Foi conduzido um trabalho experimental da vibração induzida por diversos padrões gás-líquido numa tubulação horizontal (PVC Ø3/4\'\') duplamente engastada, com água e ar como fluidos de trabalho. A partir de uma abordagem analítica, corroborada com resultados experimentais para escoamento monofásico e bifásico, estabelece-se a existência de uma relação, de natureza quadrática, entre a velocidade de atrito e o desvio padrão da aceleração. Dado que a velocidade de atrito é função do fator de atrito bifásico, um método para a sua previsão é desenvolvido. Ele prevê de maneira precisa os dados coletados; todos eles com erro percentual menor do que 30%. O método foi comparado também com dados experimentais e modelos da literatura, mostrando boa concordância. Além disso, apresenta-se uma relação entre a frequência pico da resposta e a fração de vazio homogênea. No fim, são apresentados: (i) um método de identificação de escoamento pistonado, baseado na superposição dos mecanismos de vibração por turbulência e intermitente, com desempenho mínimo de 81.8%; (ii) um método experimental para determinação da velocidade da mistura (J) e fração de vazio homogênea (β). Os melhores resultados são obtidos para os padrões disperso e pistonado, prevendo adequadamente os parâmetros J e β com erro percentual absoluto médio de 24.1% e 20.65%, respectivamente. / Flow-induced vibration is intrinsic to piping problems. For example, in the oil and gas industry the FIV phenomenon can be found in pipe flow both in upstream and downstream applications. The structural vibration response contains information about the flow phenomenology. In the case of two-phase pipe flow, experimental results show a strong influence of mixture velocity, void fraction and flow pattern on pipe structural dynamics. However, efforts to obtain information of the flow from pipe response have been scanty. The goal of this study is to develop two-phase flow parameters predictive methods based on the structural pipe response. An experimental study of flow-induced vibration was carried out for several flow patterns in a clamp-clamp straight pipe (PVC Ø3/4\'\'), with air and water as working fluids. From an analytical approach, a quadratic relationship between shear velocity and standard deviation of acceleration is proposed and validated against the experimental data of single and two-phase flow. Since the shear velocity depends on the friction factor, a method to predict two-phase friction factor is presented. The method predicts accurately our experimental data with a mean absolute error up to 30%. Good agreement was also found when it was compared with some models and experimental data from the literature. Furthermore, an expression to correlate peak frequency and homogeneous void fraction as a function of added mass is offered. Finally, we present: (i) a slug flow identification technique based on the superposition of the turbulence and intermittent flow-induced vibration mechanisms, with performance of 81.8% and (ii) an experimental methodology to estimate mixture velocity (J) and homogeneous void fraction (β). The latter method shows better agreement for dispersed and slug flow-patterns, predicting J and β with a mean absolute error of 24.1% e 20.65%, respectively.

Os resultados de uma simulação numérica são apresentados para amplitudes de vibração induzidas por um escoamento transversal num feixe tubular no regime de instabilidade fluidelástica.O feixe tubular considerado tem geometria e características iguais às de uma instalação equivalente descrita na literatura, para a qual estão disponíveis as medições experimentais das amplitudes de vibração no regime de instabilidade elástica.O arranjo tipo triângulo rodado tem uma relação passo/diâmetro de 1,375 e consiste de um tubo móvel cercado por 134 tubos rígidos.A simulação numérica foi efetuada através de um software comercial de CFD (Computational Fluid dynamics).Para a região em torno de cada tubo foi considerada uma malha com dimensões do elemento crescendo geometricamente na direção normal ao tubo com fator de crescimento 1,13 , sendo a dimensão do elemento adjacente ao tubo igual a 0,1% do diâmetro externo do tubo.Na simulação numérica o escoamento foi considerado incompressível, monofásico, turbulento e bidimensional. Os dados do escoamento foram considerados idênticos aos das experiências da instalação descrita na literatura.Os resultados obtidos para as amplitudes pela simulação numérica são comparados com os resultados obtidos experimentalmente na instalação acima citada.Os desvios da maioria dos valores calculados em relação aos valores experimentais estão numa faixa aceitável. Isto mostra que existe a possibilidade de utilização, num futuro próximo, de CFD para análise deste tipo de problemas. / Results from a numerical simulation are reported for amplitudes of cross-flow induced vibrations at the fluid elastic instability regime in a tube bank. The tube bank has identical geometry and characteristics as for an experimental facility described in the literature, for which there are experimental measurements of the amplitudes of vibrations at the fluid elastic instability regime.The rotated triangular array has a pitch ratio of 1.375 and consists of 1 movable tube surrounded by 134 rigid tubes. The numerical simulations were accomplished with a commercial CFD (Computational Fluid Dynamics) software. For the region around each tube, a mesh with elements dimensions growing geometrically normal to the tube was considered, with growing factor 1.13, and the dimension for the element adjacent to the tube wall was set to 0.1% of the tube external diameter. The flow was considered incompressible, monophasic, turbulent and two-dimensional for the numerical simulation. The flow data considered were the same as for the experiments at the facility. The results presented in this paper for the amplitudes obtained by numerical simulation are compared with the experimental results obtained in the above mentioned experimental facility.The differences between the calculated values and the experimental values are acceptable. This show that in the near future there is the possibility to use CFD for these kind of problems.

This research focuses on developing sensors for properties of aerodynamic interest (i.e., flow and pressure) based on low-cost polymeric materials and simple fabrication processes. Such sensors can be fabricated in large arrays, covering the surface of airfoils typically used in unmanned vehicles, allowing for the detection of flow separation. This in turn potentially enables, through the use of closed-loop control, an expansion of the flight envelope of these vehicles. A key advance is compensation for the typically inferior performance of these low cost materials through both careful design as well as new readout methods that reduce drift, namely a readout methodology based on aeroelastic flutter. An all-polymer micromachined piezoresistive flow sensor is fabricated, based on a flexible polyimide substrate and an elastomeric piezoresistive composite material. The flow sensor comprises a cantilever that is extended into the embedding flow; flow-induced stress on the cantilever is sensed through the piezoresistive composite material. Increasing the sensitivity of the sensor is achieved by either utilizing a long single-cantilever beam or using a dual-cantilever beam supporting a flap extending into the flow. In the latter case, the sensor demonstrates increased sensitivity with a reduced cantilever length. The increase in sensitivity helps to reduce sensor drift, which in turn is further reduced by a new measurement method, the vibration amplitude measurement method. In this drift reduction measurement method, the flow-induced vibration amplitude of the sensor structure (i.e., the amplitude of the aeroelastic flutter induced by the flow), instead of the absolute value of cantilever deflection, is measured in order to find the flow rate. Measurement of this relative resistance change instead of the absolute resistance in the piezoresistor rejects common-mode drift and greatly reduces overall drift. Experimental results verify the expected drift reduction. Sensor drift is also reduced when the elastomeric piezoresistive material is replaced by a Pt thin film piezoresistor. Development of pressure sensors based on polymers proceeds by encapsulating a reference cavity within a multilayer polymer structure and forming capacitor plates on the polymeric membranes encapsulating the cavity. Measuring the capacitance change induced by changes in the embedding pressure (which cause changes in the positions of the bounding polymeric membranes) enables calculation of the pressure. The use of polymeric membranes requires understanding the leakage rate of gas into the reference cavity, which is a source of pressure drift. Developing a polymer-based pressure sensor that solves the problem of sensor drift as a result of gas permeation entails the fabrication of a silicon pressure reference cavity embedded in the polymer substrate, which results in a more hermetic and lower drift sensor while preserving the flexibility of the embedding polymer. Both wired and wireless versions of pressure and flow sensors of these types were developed and characterized. Further, the sensors were characterized on airfoils and their performance in a wind tunnel was determined.

A vibração induzida por escoamento é parte intrínseca do transporte de fluidos. Por exemplo, na indústria de petróleo e gás esse fenômeno pode ser encontrado em tubulações, tanto no setor upstream, quando downstream. Essas vibrações são produto das forças geradas pelo escoamento e, portanto, carregam informações sobre sua fenomenologia. No caso de escoamento bifásico em tubo, resultados experimentais indicam forte influência da velocidade da mistura, fração de vazio e padrão de escoamento no comportamento dinâmico da estrutura. Contudo, pouco foi feito na tentativa de obter informações do escoamento a partir da reposta estrutural. Assim, o objetivo do presente estudo é desenvolver métodos para a previsão dos parâmetros do escoamento baseados na resposta de um tubo submetido a escoamento bifásico. Foi conduzido um trabalho experimental da vibração induzida por diversos padrões gás-líquido numa tubulação horizontal (PVC Ø3/4\'\') duplamente engastada, com água e ar como fluidos de trabalho. A partir de uma abordagem analítica, corroborada com resultados experimentais para escoamento monofásico e bifásico, estabelece-se a existência de uma relação, de natureza quadrática, entre a velocidade de atrito e o desvio padrão da aceleração. Dado que a velocidade de atrito é função do fator de atrito bifásico, um método para a sua previsão é desenvolvido. Ele prevê de maneira precisa os dados coletados; todos eles com erro percentual menor do que 30%. O método foi comparado também com dados experimentais e modelos da literatura, mostrando boa concordância. Além disso, apresenta-se uma relação entre a frequência pico da resposta e a fração de vazio homogênea. No fim, são apresentados: (i) um método de identificação de escoamento pistonado, baseado na superposição dos mecanismos de vibração por turbulência e intermitente, com desempenho mínimo de 81.8%; (ii) um método experimental para determinação da velocidade da mistura (J) e fração de vazio homogênea (β). Os melhores resultados são obtidos para os padrões disperso e pistonado, prevendo adequadamente os parâmetros J e β com erro percentual absoluto médio de 24.1% e 20.65%, respectivamente. / Flow-induced vibration is intrinsic to piping problems. For example, in the oil and gas industry the FIV phenomenon can be found in pipe flow both in upstream and downstream applications. The structural vibration response contains information about the flow phenomenology. In the case of two-phase pipe flow, experimental results show a strong influence of mixture velocity, void fraction and flow pattern on pipe structural dynamics. However, efforts to obtain information of the flow from pipe response have been scanty. The goal of this study is to develop two-phase flow parameters predictive methods based on the structural pipe response. An experimental study of flow-induced vibration was carried out for several flow patterns in a clamp-clamp straight pipe (PVC Ø3/4\'\'), with air and water as working fluids. From an analytical approach, a quadratic relationship between shear velocity and standard deviation of acceleration is proposed and validated against the experimental data of single and two-phase flow. Since the shear velocity depends on the friction factor, a method to predict two-phase friction factor is presented. The method predicts accurately our experimental data with a mean absolute error up to 30%. Good agreement was also found when it was compared with some models and experimental data from the literature. Furthermore, an expression to correlate peak frequency and homogeneous void fraction as a function of added mass is offered. Finally, we present: (i) a slug flow identification technique based on the superposition of the turbulence and intermittent flow-induced vibration mechanisms, with performance of 81.8% and (ii) an experimental methodology to estimate mixture velocity (J) and homogeneous void fraction (β). The latter method shows better agreement for dispersed and slug flow-patterns, predicting J and β with a mean absolute error of 24.1% e 20.65%, respectively.

Flow-induced vibration caused by fully developed pipe flow has been recognized, but not fully investigated under turbulent conditions. This thesis focuses on the development of a numerical Fluid-Structure Interaction (FSI) model that will help define the relationship between pipe wall vibration and the physical characteristics of turbulent flow. Commercial FSI software packages are based on Reynolds Averaged Navier-Stokes (RANS) fluid models, which do not compute the instantaneous fluctuations in turbulent flow. This thesis presents an FSI approach based on Large Eddy Simulation (LES) flow models, which do compute the instantaneous fluctuations in turbulent flow. The results based on the LES models indicate that these fluctuations contribute to the pipe vibration. It is shown that there is a near quadratic relationship between the standard deviation of the pressure field on the pipe wall and the flow rate. It is also shown that a strong relationship between pipe vibration and flow rate exists. This research has a direct impact on the geothermal, nuclear, and other fluid transport industries.

A wave cavity resonator (WCR) is investigated to determine the suitability of the device as an energy harvester in rivers or tidal flows. The WCR consists of coupling between self-excited oscillations of turbulent flow of water in an open channel along the opening of a rectangular cavity and the standing gravity wave in the cavity. The device was investigated experimentally for a range of inflow velocities, cavity opening lengths, and characteristic depths of the water. Determining appropriate models and empirical relations for the system over a range of depths allows for accuracy when designing prototypes and tools for determining the suitability of a particular river or tidal flow as a potential WCR site. The performance of the system when coupled with a wave absorber/generator is also evaluated for a range piston strokes in reference to cavity wave height. Video recording of the oscillating free-surface inside the resonator cavity in conjunction with free-surface elevation measurements using a capacitive wave gauge provides representation of the resonant wave modes of the cavity as well as the degree of the flow-wave coupling in terms of the amplitude and the quality factor of the associated spectral peak. Moreover, application of digital particle image velocimetry (PIV) provides insight into the evolution of the vortical structures that form across the cavity opening. Coherent oscillations were attainable for a wide range of water depths. Variation of the water depth affected the degree of coupling between the shear layer oscillations and the gravity wave as well as the three-dimensionality of the flow structure. In terms of the power investigation, conducted with the addition of a load cell and linear table-driven piston, the device is likely limited to running low power instrumentation unless it can be up-scaled. Up-scaling of the system, while requiring additional design considerations, is not unreasonable; large-scale systems of resonant water waves and the generation of large scale vortical structures due to tidal or river flows are even observed naturally. / Graduate / 0547 / 0548 / reaumejd@uvic.ca

The presented diploma thesis focuses on flow-induced vibrations of a tube. The main aim and benefit is the analysis of tube stiffness in contact with the other one and the following use of obtained values and characteristics in CFD simulations. The work can be divided into three parts. The first part is about the current state of knowledge of flow-induced vibrations. It introduces the basic mechanisms of vibration and methods for their suppression. The second part deals with the determination of stiffness of defined geometry tube including the collision with the other tube. The final part demonstrates and evaluates the application of obtained characteristics in CFD simulations.

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.