Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2007. / Includes bibliographical references (p. 73-74).

This thesis details the design and construction of an anechoic chamber for acoustic testing and measurements of large UAS propellers. Three propellers are considered, as they are common propeller designs used for large UAS today. The knowledge and practices involved with acoustic testing and measurements in anechoic chambers, as well as the results of noise studies related to large UAS, are not widely available due in large part to the limited availability and use of large UAS in the public domain. Using established principles related to fundamental acoustic theory and propeller noise, the aeroacoustic noise from large UAS propellers was measured to study and evaluate the reduction in total aerodynamic noise. This data and research provides the ability to evaluate propeller noise in relation to the overall detectability of large unmanned aircraft systems.

An experimental investigation of non-uniform flow past a 1.615 foot, 3-bladed propeller was conducted in the Virginia Tech 6 foot by 6 foot Stability Wind Tunnel. The free stream velocity was 44.5 ft/sec and the propeller rpm 1400. A screen disk consisting of two circular meshes, one 15 inches in diameter and the other 5, along with a 30 degree wedge having a 7.5 inch radius, was used to create the non-uniform inflow. The screen disk was chosen to simulate a wake flow behind a slender body with an attached appendage. The propeller was operated at self-propelled mode with respect to the drag of the screen disk. Several types of measurements were completed on the propeller and the near wake. First, the propeller performance quantities were measured. The second type of measurements were the mean flow quantities, which included the mean velocities and static pressures. These were obtained by using a five hole yawhead probe. The third type of measurements were made with an x-wire probe, constant temperature anemometer and an r.m. s. meter. These allowed all the turbulence quantities, intensities and shear stresses, to be obtained. All turbulence quantities were averaged in the peripheral direction. The results of the mean and turbulent flow under the non-uniform flow condition are documented and discussed in detail. The 3-D non-uniform inflow caused the location of the maximum thrust to be shifted from . 7R, previously found for uniform inflow for the same propeller, to .88R while the location of maximum swirl was shifted inward from .6R to .5R. The turbulence quantities were sensitive to the non-uniform mean inflow and the upstream turbulence created by the screen disk, especially in the wake of the wedge region. This was generally observed in the form of higher turbulence intensities and shear stresses. This data can be used to verify and refine turbulent transport models and computational methods for flows of this type. / M.S.

An experimental investigation of the near wake of a five bladed 15.50 inch (393.75 mm) diameter DTNSRDC 4767A marine propeller was conducted in the VPI Stability tunnel at an advance ratio of 0.95 in a uniform free stream at 20 ft/s (6.1 m/s). Several types of data were obtained. First, the performance characteristics, thrust, torque, and efficiency, were documented using a six component strain gage balance located in the motor housing. Secondly, the mean static pressures, mean flow velocity components, and flow angularity were measured by a five port yawhead probe. The third type of measurement was made with a straight hot-wire anemometer to find mean and turbulence intensity magnitudes averaged behind the propeller disk. These measurements were made at 21 radial locations and 5 downstream locations: X/D=0.025, X/D=0.200, X/D=0.300, X/D=0.400, X/D=0.500. Finally, the wake from an individual blade was studied by sampling the hot-wire signal at 240 fixed intervals following a constant phase, once per revolution trigger. The samples were stored on a microcomputer operated as a digital storage oscilloscope. These signals were phase averaged to yield the turbulent and mean velocities across the blade wake at ten radial locations. The slipstream (wake) of the propeller was found to contract in the downstream direction due to pressure relaxation. High swirl velocities were found near the hub, while the region of maximum thrust was typically around 0.6R. The individual blade wake data revealed very strong turbulence intensities (up to 32 percent of free stream) in the wake of each blade with relatively low turbulence between the blades. / Master of Science

The finite element method in the form of the weak Galerkin formulation with the penalty function method was applied to several problems of axisymmetric turbulent flows including flow through a sudden pipe expansion, the stern region flow of a slender body, and flows past ducted and nonducted propellers in action. The coupled set of the Reynolds time-averaged Navier-Stokes equations and two turbulence transport equations for the turbulent kinetic energy and its rate of dissipation was solved by L/U decomposition and successive substitution with relaxation. An existing finite element code was modified with a low Reynolds number form for an appropriate treatment of wall influences on turbulence transport, which produces a better solution and provides an easier imposition of boundary conditions by solving up to wall with no slip boundary conditions. The two-equation turbulence model with the wall modification was first successfully tested by solving the turbulent flow through a sudden pipe expansion. The numerical simulation of the stern region flow of a streamlined body resulted in an excellent agreement with the measured data in terms of the mean-flow and turbulence quantities. Turbulent shear flows past a propeller at the rear end of the same slender body, modeled by an actuator disk, were successfully solved at two rotational speeds, self-propelled and 100% over-thrusted, using the same two-equation model. And finally, comparisons of the wake behind a propeller were made for the self-propelled conditions of a ducted and nonducted propeller on the same streamlined body. / Ph. D.

A two-dimensional Boundary Element Method (BEM) is developed to study the strongly nonlinear interaction between a surface-piercing body and the free-surface. The scheme is applied to problems with and without the possibility of ventilation resulting from the motion and geometric configuration of the surface-piercing body. The main emphasis of this research work is on the development of numerical methods to improve the performance prediction of surface-piercing propellers by including the whole range of free-surface nonlinearities. The scheme is applied to predict the ventilated cavity shapes resulting from the vertical and rotational motion of a blade-section with fully nonlinear free-surface boundary conditions. The current method is able to predict the ventilated cavity shapes for a wide range of angles of attack and Froude numbers, and is in good agreement with existing experimental results. Through a comparison with a linearized free-surface method, the current method highlights the shortcomings of the negative image approach used commonly in two-dimensional and three-dimensional numerical methods for surface-piercing hydrofoils or propellers. The current method with all its capabilities makes it a unique contribution to improving numerical tools for the performance prediction of surface-piercing propellers. The scheme is also applied to predict the roll and heave dynamics of two-dimensional Floating Production Storage and Offloading (FPSO) vessel hull sections within a potential flow framework. The development of the potential flow model is aimed at validating the free-surface dynamics of an independently developed Navier Stokes Solver for predicting the roll characteristics of two-dimensional hull sections with bilge keels. / text

A escolha do propulsor é uma etapa-chave no projeto de um navio. Muito do que se espera qualitativamente do desempenho de uma embarcação implica em economia de energia, em condições de operação e habitabilidade adequadas à tripulação, e em baixo custo de manutenção dos elementos estruturais e dos equipamentos. Essas questões estão diretamente relacionadas ao aproveitamento de combustível pelo sistema propulsivo e à propagação de vibração, cabendo ao propulsor um papel significativo para a performance do navio em ambos os aspectos. Por esta razão, a dissertação propõe a avaliação de propulsores navais com respeito à excitação de vibração e à eficiência, quando atuando em esteira não uniforme. A dissertação inicia-se com uma abordagem resumida especificamente sobre os estudos já realizados sobre indução de vibração pelo propulsor focados nas chamadas forças de mancal. Em seguida, revisam-se os assuntos pertinentes ao projeto de propulsor, isto é, definição de sua geometria, de seus coeficientes de operação, e dos métodos teóricos e computacionais utilizados para estudar seu comportamento hidrodinâmico. A metodologia do trabalho fundamenta-se no estudo paramétrico da geometria do hélice, objetivando identificar a influência de cada um dos parâmetros de projeto do propulsor nos dois aspectos destacados no início. As diversas configurações geométricas são submetidas a campos de velocidades advindos de diferentes navios, que representam três grupos de embarcações (navios série 60, porta-containers e navios-tanque), com o intuito de verificar as diferentes tendências de comportamento possíveis. Para a execução computacional, elabora-se uma rotina encarregada de sistematizar o processo de alterações geométricas, encaminhar os numerosos casos à análise hidrodinâmica, realizar o processo de integração casco-hélice e o pós-processamento dos resultados. A análise hidrodinâmica citada é feita através do uso de um software comercial, que, baseado na teoria do escoamento potencial, aplica o método dos painéis para a resolução do escoamento ao redor do propulsor. Os esforços excitados pelo hélice são traduzidos em critérios objetivos, baseados na transmissão de vibração através do eixo, que, associados ao critério de eficiência propulsora e à restrição relativa à ocorrência de cavitação, avaliam os casos e identificam-se o comportamento dos parâmetros de projeto. Obtém-se, como conclusão, uma metodologia de avaliação aplicável em outros casos de propulsores e navios. / The propeller choice is a key-step of the ship design. The high quality of the vessel performance requires energy economy, appropriated operating and environmental conditions for the crew, and low maintenance costs of structural elements and equipment. These questions consider directly fuel consumption by the propulsion system and the transmitted vibration, regarding the propeller an important role in the ships performance about both attributes. For this reason, the evaluation of marine propellers, regarding the induced vibration and the propulsive efficiency under a non-uniform inflow, is proposed. The study begins with a briefly state of the art about the propeller induced vibration focused in bearing forces. Then, a propeller design overview is made about subjects such as geometry definition, operation coefficients, and theoretical and computed methods for studying its hydrodynamic behavior. The methodology is based on a parametric study of the propeller geometry, in order to identify the influence of each of the propeller design parameters in both aspects highlighted in beginning. The several geometric configurations are submitted to the wake fields from different ships, that represent three groups of vessels (60 series, containers and tankers), then different tendencies of behavior can be expected. For computational execution, a routine is in charge of systematizing the process of geometrical parameterization, send the cases to the hydrodynamic analysis, make the hull-propeller integration and post process the data. The hydrodynamic analysis is compelled by a HSVA® software, which applies the panel method in the propeller flow, based on potential flow theory. The propeller induced bearing forces are converted in objective criteria, based on vibration transmission through the shaft, which, combined with the propulsive efficiency criteria and the cavitation restriction, evaluate the propeller geometric configurations. As a conclusion, a propeller evaluation methodology applicable to another kind of propeller series and wake fields is obtained.

O trabalho mostra os resultados de uma série de medições de desempenho propulsivo de um comboio no rio Araguaia, constituído de um empurrador bihélice de potência instalada de 448kW e duas chatas de 530 t de deslocamento cada. O empurrador teve, durante o período de medições, dois tipos de propulsores diferentes: da série B-Troost, mais convencional, e da série Kaplan em dutos. Os resultados de escala real foram analisados fazendo uso, inclusive, de resultados com modelos em tanques de provas, com o objetivo de descobrir os problemas e identificar os melhores procedimentos para o projeto de hélices de embarcações fluviais de cargas. Levando em consideração as características operacionais com alto carregamento das pás dos hélice fluviais, foi proposto um tratamento diferenciado daquele tradicionalmente aplicado em hélices de embarcações marítimas convencionais. Ao final, foi verificado que existem métodos adequados de estimativas de resistências ao avanço de comboios fluviais, mas que existem problemas nas estimativas dos coeficientes propulsivos, o que influencia decisivamente a qualidade dos projetos dos hélices fluviais. Com relação à geometria das pás dos hélices, concluiu-se que os hélices fluviais devem apresentar, em termos gerais, pequenos diâmetros, grandes razões de áreas expandidas, pás mais espessas, especialmente nas pontas, simetria do contorno das pás e ausência de caimento. As análises mostraram, também, as vantagens da utilização de hélices em dutos, assim como constataram que as séries sistemáticas de hélices podem ser utilizadas com pleno êxito em projetos de hélices de embarcações fluviais. / This work shows the results of a series of measurements of propulsive performance of a push-tow in the Araguaia river, with a 448kW twin-screw pusher and two 530t barges. During the measurements the pusher was fitted with two different types of propellers: firstly with a more conventional B-Troost one and later with a Kaplan ducted propeller. The full scale results were analyzed by using results of towing tank tests in order to find out the problems and identify the best procedures for the design of propellers of inland vessels. Taking into consideration the operational characteristics of heavily loaded blades of inland vessel propellers, it has been proposed a differentiated treatment compared to that usually applied on conventional marine propellers. At the end, it was verified that there exist good methods of estimating push-tow resistances, but there are problems in estimating the propulsive coefficients, and these influence decisively the quality of inland propeller design. Regarding the blades geometry of the propeller, it was concluded that inland propellers should have small diameters, great expanded area ratios, thicker blade sections, especially in the tips, no skew and no rake. The analysis showed, also, the advantages of the ducted-propellers in inland vessels, as well as it verified that the propeller systematical series can be used successfully for the selection of such propellers.

Este trabalho aborda o projeto de hélices navais auxiliado por computador, particularizando-os para a aplicação no sistema de propulsão de veículos autônomos de superfície (ASVs). São apresentadas as principais aplicações e características do casco demais sistemas que compõem os ASVs. Em seguida, trata-se da análise dos parâmetros principais que definem a geometria de um hélice naval. É proposta uma ferramenta numérica voltada à geração da superfície do hélice e do seu modelo sólido, a partir dos perfis transversais da pá, cuja distribuição radial é originada em dados de tabelas de séries sistemáticas. O trabalho é complementado por uma apresentação e análise dos métodos principais considerados para a manufatura auxiliada por computador de hélices que podem ser empregados tanto em ASVs como em outros veículos aquáticos não tripulados. / This work deals with the computer aided design of marine propellers applied to the propulsion system of autonomous surface crafts (ASVs). The main applications and component systems of ASVs are introduced. An analysis of the propeller main geometric parameters is performed, and a numerical tool is proposed for the surface and solid model generation using data provided by the propeller systematic series for the sectional profile radial description. Finally, it is presented the introduction and analysis of the computer aided manufacturing processes considered for the propulsion of ASVs and other unmanned aquatic vehicles.