The laminar flow over a prolate spheroid was investigated via flow visualization and Laser-Doppler Velocimetry. Experiments were conducted in a water tunnel and the flow was visualized with dyes. The measurement of three-dimensional boundary layers required a special design of the laser optics. Attention was focused in the neighborhood of three-dimensional separation. The Vortex-Lattice method was employed to calculate the inviscid flow and the development of separated vortex sheets over a prolate spheroid. An approximate-method based on the assumption of local similarity was used to solve the boundary layer equations and calculate the line of open separation. A condition of vortex shedding along separation is proposed. The two schemes, viscous and inviscid, interact through the line of separation which is allowed to displace as the wake grows. Results are compared with flow visualization data for laminar separation and pressure data for turbulent separation. / Ph. D.

Pulsed ultrasound Doppler velocimetry proved to be capable of measuring velocities accurately (relative error less than 0.5 percent). In this research, the limitations of the method are investigated when measuring: in channels with a small thickness compared to the transducer diameter, at low velocities and in the presence of a flow reversal area. A review of the fundamentals of pulsed ultrasound Doppler velocimetry reveals that the accuracy of the measured velocity field mainly depends on the shape of the acoustic beam through the flow field and the intensity of the echo from the incident particles where the velocity is being measured. The ultrasonic transducer turned out to be most critical component of the system. Fundamental limitations of the method are identified. With ultrasonic beam measurements, the beam shape and echo intensity is further investigated. In general, the shape of the ultrasonic beam varies depending on the frequency and diameter of the emitter as well as the characteristics of the acoustic interface that the beam encounters. Moreover, the most promising transducer to measure velocity profiles in small channels is identified. Since the application of pulsed ultrasound Doppler velocimetry often involves the propagation of the ultrasonic burst through Plexiglas, the effect of Plexiglas walls on the measured velocity profile is analyzed and quantified in detail. The transducers ringing effect and the saturation region caused by highly absorbing acoustic interfaces are identified as limitations of the method. By comparing measurement results in the small rectangular channel to numerically calculated results, further limitations of the method are identified. It was not possible to determine velocities correctly throughout the whole channel at low flow rates, in small geometries and in the flow separation region. A discrepancy between the maximum measured velocity, velocity profile perturbations and incorrect velocity determination at the far channel wall were main shortcomings. Measurement results are improved by changes in the Doppler angle, the flow rate and the particle concentration. Suggestions to enhance the measurement system, especially its spatial resolution, and to further investigate acoustic wave interactions are made.

The technologies of urban wind turbines have been rapidly developed in recent years, but urban wind turbines have not found a wide application due to the limitations of their designs. The power output of urban wind turbine is significantly affected by urban terrain, which can cause low speed flow with frequent change of its direction. Thus, there is a need for a new wind turbine to meet the requirements of an urban wind turbine. In this study, a novel wind turbine for urban areas was designed and developed. The investigations of the novel urban wind turbine were carried out by using computational fluid dynamic (CFD) simulations and wind tunnel tests. The results from the investigation have shown that the novel wind turbine has a great potential to harvest wind energy in urban areas. A detailed study of effects of each parameter on wind energy concentration of the novel wind turbine was carried out with CFD simulations. According to the simulation results, the shroud structure of the novel wind turbine was modified and the dimensions of the final structure were identified. It was determined that the capability of wind energy concentration of the novel wind turbine shroud has been significantly improved through the structure optimisations. Furthermore, guide vane and impulse turbine were implemented in the novel wind turbine. The flow characteristics through the guide vane was studied and discussed. It was found that the wind flow characteristics can be properly modified by implementing guide vane and the structure of impulse turbine was suitable to be implemented in the novel wind turbine due to the flow characteristic through the guide vane.

Approved for public release; distribution is unlimited. / Flapping-wing propulsion was studied experimentally through Laser Doppler Velocimetry. Measurements were both time-averaged and unsteady, and were conducted on a Micro-Air Vehicle (MAV) model developed at NPS by Professors Max Platzer and Kevin Jones. The objective of this work was to further understanding of the aerodynamics of flapping-wing propulsion. In specific, this study examined separation control on the leading fixed wing due to entrainment by the trailing flapping wings. Further, a study of wake topology examined differences between the optimal and off-optimal cases. Experimental studies took place in the NPS 5' x 5' low speed wind tunnel. The model was supported on a test stand and LDV measurements of the flow field were taken. Studies were made at varying freestream velocities, angles of attack, and flapping frequencies. The test stand was instrumented with force balances to show forces in both the streamwise and vertical directions. / Ensign, United States Naval Reserve

A thesis submitted to the Faculty of Science, University of the Witwatersrand in fulfillment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 3 April 2017. / The effect of suction and blowing at the base on the horizontal spreading under gravity of a two-dimensional thin fluid film and an axisymmetric liquid drop is in- vestigated. The velocity vn which describes the suction/injection of fluid at the base is not specified initially. The height of the thin film satisfies a nonlinear diffusion equation with vn as a source term. The Lie group method for the solution of partial differential equations is used to reduce the partial differential equations to ordinary differential equations and to construct group invariant solutions. For a group invari- ant solution to exist, vn must satisfy a first order linear partial differential equation. The two-dimensional spreading of a thin fluid film is first investigated. Two models for vn which give analytical solutions are analysed. In the first model vn is propor- tional to the height of the thin film at that point. The constant of proportionality is β (−∞ < β < ∞). The half-width always increases to infinity as time increases even for suction at the base. The range of β for the thin fluid film approximation to be valid is determined. For all values of suction and a small range of blowing the maximum height of the film tends to zero as time t → ∞. There is a value of β corresponding to blowing for which the maximum height remains constant with the blowing balancing the effect of gravity. For stronger blowing the maximum height tends to infinity algebraically, there is a value of β for which the maximum height tends to infinity exponentially and for stronger blowing, still in the range for which the thin film approximation is valid, the maximum height tends to infinity in a finite time. For blowing the location of a stagnation point on the centre line is determined by solving a cubic equation approximately by a singular perturbation method and then exactly using a trigonometric solution. A dividing streamline passes through the stagnation point which separates the flow into two regions, an upper region consisting of fluid descending due to gravity and a lower region consisting of fluid rising due to blowing. For sufficiently strong blowing the lower region fills the whole of the film. In the second model vn is proportional to the spatial gradient of the height with constant of proportionality β∗ (−∞ < β∗ < ∞). The maximum height always decreases to zero as time increases even for blowing. The range of β∗ for the thin fluid film approximation to be valid is determined. The half-width tends to infinity algebraically for all blowing and a small range of weak suction. There is a value of β∗ corresponding to suction for which the half-width remains constant with the suction balancing the spreading due to gravity. For stronger suction the half-width tends to zero as t → ∞. For even stronger suction there is a value of β∗ for which the half-width tends to zero exponentially and a range of β∗ for which it tends to zero in a finite time but these values lie outside the range for which the thin fluid film approximation is valid. For blowing there is a stagnation point on the centre line at the base. Two dividing streamlines passes through the stagnation point which separate fluid descending due to gravity from fluid rising due to blowing. An approximate analytical solution is derived for the two dividing streamlines. A similar analysis is performed for the axisymmetric spreading of a liquid drop and the results are compared with the two-dimensional spreading of a thin fluid film. Since the two models for vn are still quite general it can be expected that general results found will apply to other models. These include the existence of a divid- ing streamline separating descending and rising fluid for blowing, the existence of a strength of blowing which balances the effect of gravity so the maximum height remains constant and the existence of a strength of suction which balances spreading due to gravity so that the half-width/radius remains constant. / MT 2017

For aerospace and naval applications where low radiated noise levels are a requirement, rotor noise generated by inflow turbulence is of great interest. Inflow turbulence is stretched and distorted as it is ingested into a thrusting rotor which can have a significant impact on the noise source levels. This thesis studies the distortion of subsonic, high Reynolds number turbulent flow, with viscous effects ignored, that occur when a rotor is embedded in a turbulent boundary layer. The analysis is based on Rapid Distortion Theory (RDT), which describes the linear evolution of turbulent eddies as they are stretched by a mean flow distortion. Providing that the gust does not distort the mean flow streamlines the solution for a mean flow with shear is found to be the same as the solution for a mean potential flow with the addition of a potential flow gust. By investigating the inflow distortion of small-scale turbulence for various simple flows and rotor inflows with weak shear, it is shown that RDT can be applied to incompressible shear flows to determine the flow distortion. It is also shown that RDT can be applied to more complex flows modeled by the Reynolds Averaged Navier Stokes (RANS) equations. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.

This study assesses the viability of using a towfish mounted ADV for quantifying water velocity fluctuations in the Florida Current relevant to ocean current turbine performance. For this study a motion compensated ADV is operated in a test flume. Water velocity fluctuations are generated by a 1.3 cm pipe suspended in front of the ADV at relative current speeds of 0.9 m/s and 0.15 m/s, giving Reynolds numbers on the order of 1000. ADV pitching motion of +/- 2.5 [degree] at 0.3 Hz and a heave motion of 0.3 m amplitude at 0.2 Hz are utilized to evaluate the motion compensation approach. The results show correction for motion provides up to an order of magnitude reduction in turbulent kinetic energy at frequencies of motion while the IMU is found to generate 2% error at 1/30 Hz and 9% error at 1/60 Hz in turbulence intensity. / by James William Lovenbury. / Thesis (M.S.C.S.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Este trabalho aborda o escoamento ao redor de cilindros flexíveis com grande razão de aspecto, representando os riser utilizados na indústria petrolífera. O escoamento foi dividido em seções bidimensionais ao longo do comprimento do riser. O método dos vórtices discretos foi utilizado para estimativa dos coeficientes hidrodinâmicos nas seções correspondentes e o acoplamento se dá através da dinâmica estrutural. Esta dinâmica é resolvida pelo método dos elementos finitos implementado no código Anflex (Mourelle et al. (2001)). Processamento paralelo é utilizado para acelerar o desempenho do método numérico. Um esquema master-slave (\"mestre-escravo\") utilizando MPI (Message Passing Interface1) é utilizado para que seja explorado o paralelismo da modelagem. As seções hidrodinâmicas são igualmente divididas ao longo dos nós de um cluster de computadores utilizado nos cálculos. Cada nó do cluster (núcleo de processamento) resolve o escoamento nas seções hidrodinâmicas necessárias. As forças hidrodinâmicas atuando nas seções correspondentes são enviadas ao processo mestre que também é responsável pela resolução da dinâmica estrutural. Uma das contribuições do presente trabalho é a possibilidade de análise de risers em regime pós-crítico, através da imposição do ponto de separação da camada-limite baseado em resultados experimentais, e da modelagem de casos com risers em tandem. O Método dos Vórtices Discretos (MVD) está detalhado de forma a facilitar a implementação computacional, levando em consideração a possibilidade de estudo de interferência entre esteiras de múltiplos corpos. Como primeira aproximação, foram simulados, casos de cilindros rígidos fixos e em base elástica para os quais foram examinadas as amplitudes máximas de oscilação e os coeficientes de arrasto e sustentação. Posteriormente, o MVD foi integrado ao Anflex dando origem ao AnflexCFD, com capacidade de processamento paralelo da parte correspondente ao CFD. Os resultados obtidos numericamente foram comparados a resultados experimentais realizados em laboratório. A metodologia de utilização do MVD para cálculo dos coeficientes hidrodinâmicos é baseada na comparação com resultados experimentais obtidos em laboratório para cilindros rígidos fixos e em base elástica para os quais se observa uma aderência satisfatória com relação aos resultados obtidos numericamente. O resultado do presente trabalho foi a criação de uma ferramenta alternativa no projeto de risers de grande razão de aspecto, como uma forma de avaliação do comportamento dinâmico da estrutura submetida a diferentes perfis de corrente e, consequentemente, a estimativa do tempo de sua vida útil. A característica puramente Lagrangiana do MVD possibilita a simulação de centenas de ciclos de oscilação da estrutura sendo que para os métodos Eulerianos tradicionais de CFD, como o método dos volumes finitos e o método dos elementos finitos, a simulação necessita de um tempo computacional inviável para projeto. A aderência do modelo adotado em relação aos resultados experimentais, aliada a eficiência do MVD, é um indicativo da vantagem da utilização de métodos Lagrangianos na modelagem do escoamento ao redor de cilindros flexíveis com grande razão de aspecto, em relação aos métodos Eulerianos tradicionais. A metodologia apresentada neste trabalho pode ser aplicada utilizando outros métodos de CFD, lembrando que isto pode implicar num aumento significativo do tempo computacional necessário para uma análise. / In this work the dynamic response of a high aspect ratio flexible cylinder due to vortex shedding is numerically investigated. The model is divided in two-dimensional sections along the riser length. The discrete vortex method (DVM) is employed for the assessment of the hydrodynamic forces acting on these two-dimensional sections. The hydrodynamic sections are solved independently, and the coupling among the sections is taken into account by the solution of the structure in the time domain by the finite element method implemented in Anflex code (Mourelle et al. (2001)). Parallel processing is employed to improve the performance of the method. A master-slave approach via MPI (Message Passing Interface) is used to exploit the parallelism of the present code. The riser sections are equally divided among the nodes of the cluster. Each node solves the hydrodynamic sections assigned to it. The forces acting on the sections are then passed to the master processor, which is responsible for the calculation of the displacement of the whole structure. One of the main contributions of the present work is the possibility of simulating the flow around flexible cylinders in the pos-critical regime and around bundle of risers.

Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaf 51. / M.S.

The process of shock-induced ignition has been investigated both computa- tionally and experimentally, with particular emphasis on the concept of radical farming. The first component of the investigation contained Computational Fluid Dynamic (CFD) calculations of an ignition delay study, a 2D pre-mixed flow over flat plate at a constant angle to the freestream, and through a generic 2D scramjet model. The focal point of the investigation however examined the complex 3D flow through a generic scramjet model. Five experimental test conditions were ex- amined over flow enthalpies from 3.4 MJ/kg to 6.4 MJ/kg. All test conditions simulated flight at 21000 metres ([symbol=almost equal to] 70000 ft), while the equivalent flight Mach number varied from approximately 8.5 at the lowest enthalpy, to approximately Mach 12 at the highest enthalpy condition. The presence of H2 fuel injected in the intake caused a separated region to form on the lower surface of the model at the entrance to the combustor. A fraction of the total mass of fuel was entrained in this separated region, providing long residence times, hence increased time for the chemical reactions that lead to ignition to occur. In addition, extremely high temperatures were found to exist between each fuel jet. Both fuel and air are present in these regions, therefore the chance of ignition in these regions is high. Streamlines passing through the recirculation zone ignited within this zone, while streamlines passing between the fuel jets ignited soon after entry into the combustor. The first instance of a pressure rise from combustion was observed on the centreline of the model where the reflected bow shock around the fuel jets crossed the centreline of the combus- tor. Upstream of this location the static pressure of the flow was too low for the chemical reactions that release heat to occur. The comparison between the experimental and computational results was lim- ited due to inaccuracies in modelling the thermal state of the gas in the CFD calculations. The gas was modelled as being in a state of thermal equilibrium at all times, which incorrectly models the freestream flow from the nozzle of the shock tunnel, and also the flow downstream of oblique shock wave within the scramjet model. As a result combustion occurs sooner in the CFD calculations than in the experimental result.