Techn. Universiẗat, Diss., 2003--Berlin.

This thesis describes the development of the two-frequency Planar Doppler Velocimetry (2n-PDV) flow measurement technique. This is modification of the Planar Doppler Velocimetry (PDV) technique that allows the measurement of up to three components of the flow velocity across a plane defined by a laser light sheet. The 2n-PDV technique reduces the number of components required to a single CCD camera and iodine cell from the two CCDs in conventional PDV. This removes the error sources associated with the misalignment of the two camera images and polarisation effects due to the beam splitters used in conventional PDV. The construction of a single velocity component 2n-PDV system is described and measurements made on the velocity field of a rotating disc and an axisymmetric air jet. The system was then modified to make 3D velocity measurements using coherent imaging fibre bundles to port multiple views to a single detector head. A method of approximately doubling the sensitivity of the technique was demonstrated using the measurements made on the velocity field of the rotating disc and was shown to reduce the error level in the final orthogonal velocity components by ~40 to 50%. Error levels of between 1.5ms-1 and 3.1ms-1 depending upon observation direction are demonstrated for a velocity field of ±34ms-1. The factors that will influence the selection of a viewing configuration when making 3D PDV measurements are then investigated with the aid of a computer model. The influence of the observation direction, the magnitude of the flow velocity, and the transformation to orthogonal velocity components are discussed. A new method using additional data in this transformation is presented and experimental results calculated using four-measured velocity components are compared to those found conventionally, using only three components. The inclusion of additional data is shown to reduce the final error levels by up to 25%.

This thesis contains an experimental campaign on the practical implementation of oscillating-foil technologies. It explores two possible engineering applications of oscillating-wings: thrust-generation, and energy-extraction. The history of, benefits of, and difficulties involved in the use of oscillating-foils is discussed throughout. Many existing technologies used for thrust generation and hydrokinetic energy extraction are based on rotating blades or foils, which have evolved over decades of use. In recent years, designs that use oscillating-foils, with motions analogous to the flapping of a fish’s tail or a bird’s wing, have shown increased hydrodynamic performance compared to the traditional rotary technologies. However, these systems are complex, both in terms of the governing unsteady fluid dynamics, and the methods by which kinematics are prescribed. Simply put, system complexity and cost need to be reduced before these devices see wide-spread use. For this reason, the work contained within this thesis explores possible methods of reducing the complexity of oscillating-foil systems in an effort to contribute to their development. For thrust-generation applications, this entailed using flexible foils to create passive pitching kinematics. This was parametrically studied by testing foils of different structural properties under a range of kinematics. The results suggested that properly tuning the flexibility of the foil could enhance both the thrust generation, and the efficiency of the propulsive system. With respect to energy-harvesting applications, the reliability of a novel fully passive turbine was assessed. The prototype tested had no active control strategy, and the degreesof-freedom were not mechanically linked, greatly simplifying the design. The prototype was subjected to real-world conditions, including high turbulence levels and the wake of an upstream turbine, and displayed robust performance in most conditions. In both applications, the hydrodynamic performance of the oscillating-wings was directly measured, and particle image velocimetry was used to observe the flow topology in the wakes and boundary layers of the foils. The vortex and stall dynamics were highlighted as key flow features, and are studied in detail. / Graduate

Neste trabalho apresenta-se o estudo da transferência de massa (oxigênio) de bolhas de ar para a água, geradas por um difusor de ar, confeccionado com plástico microporoso e de fabricação nacional, em uma coluna de aeração. O processo de aeração conduziu à determinação do coeficiente volumétrico de transferência de massa, coeficiente volumétrico de transferência de massa global, e foi executado na coluna mencionada, construída em material transparente. Utilizou-se água de fonte, existente no abastecimento do Laboratório de Hidráulica Ambiental (SHS/CRHEA). Variou-se a vazão do ar no processo de aeração de 400 l/h a 2.000 l/h e o nível de água dentro da coluna de 0,50 m a 1,80 m. Optou-se pelo método químico para deaerar a água, utilizando sulfito de sódio anidro antes do início de cada ensaio. O aparelho WTW-323, um medidor de oxigênio do tipo membrana permeável, foi usado para determinar a evolução da concentração de oxigênio dissolvido na água durante todo o processo de aeração. Características hidrodinâmicas foram quantificadas, como os campos de velocidade ascensional das bolhas de ar, o diâmetro equivalente das bolhas e sua freqüência de ocorrência. Para essas quantificações utilizou-se equipamento Laser para velocimetria não-intrusiva. As características mencionadas são fundamentais para verificar as previsões para o coeficiente de transferência de massa encontradas na literatura. A coluna usada tem seção transversal quadrada de 0,19 m x 0,19 m, constante em toda sua extensão, e altura de 2,00 m. Através da determinação da eficiência de transferência de massa de oxigênio na água, variando a vazão de aeração e o nível de água na coluna, concluiu-se que a vazão entre 600 l/h e 800 l/h e nível de água de 1.80 m é que apresentou maior eficiência de transferência de massa. / The present work is a study of the oxygen mass transfer from air bubbles into water, generated by a diffuser of air, in a column of aeration. This diffuser was made of microporous plastic and produced in Brazil. The process of aeration in the column built with transparent material determined the volumetric coeficient of the mass transfer Kla. Water from the well located in the Environmental Hydraulic Laboratory (SHS/CRHEA) was used. The air flow in the process of aeration was changed from 400 l/h to 2000 l/h and the level of water, from 0,50 m to 1,80 m. The chemical method was chosen to deoxygenate water and sulfite of anhydrous sodium was used before starting each experiment. The equipment WTW-323, an oxygen gauge with permeable membrane, was used to determine the development of the oxygen concentration dissolved in water during the process of aeration. Several hydrodinamic characteristics were measured, such as the velocity range of the air bubbles, their diameter and their frequency, by using a laser equipment for non-intrusive velocimetry. These characteristics are fundamental to check the mass transfer coeficient that are in literature. The column used for the experiment had a square cross section of 0,19 m x 0,19 m in alI extension and height of 2 meters. After determination of the efficiency of the mass transfer of oxygen into water, changing the air flow rate and the level of water in the column, it was concluded that the air flow between 600 l/h and 800 l/h and the level of water of 1,80 m were the most efficient.

Cette thèse traite de l'application de l'holographie numérique dans l'axe à l'étude d'une dynamique tourbillonnaire dans un champ de houle. Lors du passage de la houle au dessus d'une structure immergée, des tourbillons se forment à ses extrémités. Ces tourbillons ont un impact fort sur la dynamique proche des structures et peuvent engendrer des problèmes d'affouillement ou de vieillissement prématuré. On s'intéresse donc à la dynamique tridimensionnelle de ces tourbillons qui sont rapidement l'objet de déformations menant à leur éclatement. Pour étudier ce mécanisme, le problème est modélisé par une géométrie simple, une plaque soumise à une houle monochromatique. Les expériences sont menées dans un canal à houle de 10 m de long et 30 cm de large. Pour mesurer la dynamique 3D on utilise une technique innovante, l'holographie numérique qui permet une mesure 3D3C au moyen d'une diode laser et d'une seule caméra. Ses principales limitations résident dans la dimension de la section du volume de mesure, qui est de l'ordre de la surface du capteur CCD, ainsi que du nombre de particules présentes dans le champ. Toutefois, l'holographie permet une résolution de l'ordre de la taille d'un pixel dans le plan du capteur CCD et de 3 à 5 fois le diamètre de la particule suivie dans la direction orthogonale au capteur. Ces mesures permettent de suivre individuellement plusieurs centaines de particules dans le champ et d'en mesurer les vitesses. Enfin des mesures complémentaires en stéréo-piv confirment les résultats obtenues par holographie et permettent l'étude du confinement du tourbillon sous l'action combinée de la surface libre et de la plaque. / This thesis deals with the use of digital in-line holography to the study of a vortex dynamics under water waves. As waves propagate above an immersed structure, vortices are formed at its edges. Those vortices have a strong impact on the flow dynamics in the vicinity of structures and can cause scouring or damages. Thus we are interested in the three-dimensional dynamics of those vortices which are quickly distorted, leading to their breakup. To study this dynamics, the physical problem is modelled by a basic geometry, a thin plate is set under monochromatic waves. Experiments are conduct within a wave flume of dimensions 10 m long and 30 cm width. To measure the 3D flow the use of an innovative technique, the digital holography which allow a 3D3C measure with only one camera and a laser diode. Its main limitations are the size of the cross-section of the sample volume and the number of particles allowed in it. However, digital holography can localize particles with a pixel sized resolution within the plans parallel to the CCD sensor and a depth resolution in the order of 3 to 5 times the particles diameter. Those measurements enable to follow the path of each particle inside the sample volume. Finally, acquisition by stereo particle image velocimetry confirms the velocities measured by holography and are used to study the interaction between the vortex and the combined action of free surface and the plate.

Further understanding the small scale coherent structures which occur in high Reynolds number turbulence would be of enormous benefit. Therefore, the aim of the current project was to make well resolved three-dimensional flow measurements of the mixing flow between counter rotating impellers, using Tomographic Particle Image Velocimetry (TPIV).TPIV software was developed, with a novel approach permitting a significant reduction in processing time, and a series of numerical accuracy studies contributing to the fundamental understanding of this new technique. Basic flow characterisation determined the local isotropy, homogeneity and expected Reynolds number scaling. A favourable comparison between planar PIV and TPIV increased confidence in the latter, which was used to assess the dynamics and topology of the dissipation scale structures. In support of previous investigations similar topology, strain rate alignment, scale-invariance, and clustering behaviours are demonstrated. Correlated high enstrophy and dissipation regions occur in the periphery of larger structures, resulting in intermittency. Geometry characterisation indicates a predominance of tube-like structures, which are observed to form from larger ribbon-like structures through unsteady breakdown and vortex roll-up. Significant correlation between intermittent fields of dissipation and enstrophy describe the fine scales effects. These relationships should pave the way for more accurate models, capable of relating small scales and large scales during the prediction of dynamically important quantities.

The objective of this research is to experimentally investigate the flow characteristics past a bileaflet mechanical heart valve (BMHV) in an anatomical model of the aorta. The measurements were made within a mock circulation loop that produced physiological pressure and flow conditions of the aorta. The velocity was measured upstream and downstream of the valve at single points using laser Doppler velocimetry and on planes using planar particle image velocimetry. Viscous and turbulent stresses were evaluated as indicators of potential blood damage. Measurements were first made with a BMHV mounted at the inlet of an axisymmetric channel, which was similar in geometry to channels previously used, and then with the BMHV mounted at the inlet of an anatomical model of the aorta. By comparing these results, the effects of the anatomical shape of the aorta on the flow past the valve were determined. It was found that the level of turbulence past the valve was significantly greater in the axisymmetric model and that the shape of the anatomical aortic sinus, in particular, was effective in reducing turbulence. Additionally, measurements with the valve mounted in three orientations at the inlet of the anatomical aorta showed that the turbulence and the viscous stresses past the valve were lower when the valve was positioned such that its line of symmetry was parallel with the plane of aorta curvature than when it was normal to it. It was further found that flow in the right coronary artery was highest when the valve was positioned with its central orifice aligned with the opening to this artery. The results of this research may be used to assist surgeons in choosing the best implantation orientation of a BMHV.

This work investigates flow measurement capabilities within meso- and micro-scaled medically relevant devices using particle image velocimetry (PIV). Medical devices can be particularly challenging to validate due to small length scales and complex geometries, which can reduce measurement accuracy by introducing noise and reducing available signal. Although the sources of such problems are often device specific, the effective outcome is a reduction in the signal-to-noise ratios (SNRs) of PIV images and correlations. This effort utilizes advanced PIV processing and post-processing techniques to establish protocols for achieving high accuracy PIV measurements in challenging flow environments. This investigation takes place within three wide-ranging medically related devices. First, channel flow in a microfluidic device is investigated to evaluate improvements in measurement accuracy gained using phase correlations in comparison to confocal microscopy. This work found substantial improvements in error with respect to the ensemble field for phase correlations while only moderate improvements were observed for confocal imaging with standard processing techniques. Secondly, an evaluation of stenting procedures was executed resulting in the first published PIV and computational fluid dynamics (CFD) joint study on bifurcating stents. This work analyzes steady flow in three bifurcation angles and four different single- and double-stenting procedures, which are clinically used in coronary bifurcations. Finally, a medical device analog was evaluated to develop a comprehensive CFD validation dataset, including a full uncertainty analysis for velocity and wall shear stress as well as estimates for pressure fields and relevant flow statistics including Reynolds stresses and dissipation. / Ph. D.

Of the potential feedstocks for biofuels, microalgae is the most promising, and raceway ponds are the most cost-effective method for growing mircoalgal biomass. Nevertheless, biofuel production from algae must be more efficient to be competitive with traditional fuels. Previous studies using arrays of airfoils, triangles, and squares at high angles of attack show an increase in mixing in raceways and can improve productivity by up to a factor of 2.2. Some researchers say increasing mixing increases growth due to the flashing light effect while others claim it is the decrease in the fluid boundary layer of the cells that increases mass transfer. Whatever the reason, increasing growth by increasing mixing is a repeatable effect that is desirable to both reduce operation costs and increase production. An experimental raceway is constructed to test the effect of a delta wing (DW) on raceway hydraulics in the laboratory using fresh-water. The DW is an isosceles triangle made of plate material that is placed at a high angle of attack in the circulating raceway flow. Results from this investigation can be scaled to larger growth facilities use arrays of DWs. Two vortices are found downstream of the DW when used in this way and create significant vertical fluid circulation. Stereo particle image velocimetry (PIV) is used to quantify and optimize the use of delta wings as a means to increase fluid mixing. Stereo PIV gives three components of velocity in a measurement plane at an instant. Three studies are performed to determine the optimal paddle-wheel speed, angle of attack, and DW spacing in the raceway based on mixing. Two new mixing quantities are defined. The first is the Vertical Mixing Index (VMI) that is based on the vertical velocity magnitude, and the second is the Cycle Time required for an algal cell to complete a cycle from the bottom to the top and back again in the raceway. The power required to circulate the flow is considered in all results. The Paddle-wheel Speed Study shows that the VMI is not a function of streamwise velocity, which makes it very useful for comparison. The Cycle Time decreases quickly with streamwise velocity then levels out, revealing a practical speed for operation that is lower than typically used and consumes only half the power. The angle of 40° is optimal from the results of the Angle of Attack Study for both VMI and Cycle Time. The third study is the Vortex Dissipation Study and is used to measure the distance downstream before the vortices dissipate. This information is used to optimize the DW spacing for profit considering the additional costs of adding DWs.

A moving contact line is the idealized line of intersection between two immiscible fluids as one displaces the other along a solid boundary. The displacement process has been the subject of a large amount of theoretical and experimental research; however, the fundamental processes that govern contact line motion are still unknown. The challenge from an experimental perspective is to make measurements with high enough resolution to validate competing theories. An experimental method has been developed to simultaneously measure interface motion, dynamic contact angles, and local fluid velocity fields using micron-resolution Particle Image Velocimetry (µPIV). Capillary numbers range from 1.7 x 10^(⁻⁴) to 6.2 x 10^(⁻⁴). Interface velocities were measured between 1.7 µm/s and 33 µm/s. Dynamic contact angles were manually measured between 1.1 µm and 120 µm from the contact line, and calculated from µPIV data to within several hundred nanometers from the contact line. Fluid velocities were measured over two orders of magnitude closer to the contact line than published values with an increase in resolution of over 3400%. The appearance of a recirculation zone similar to controversial prediction below previously published limits demonstrates the power and significance of the method.