Aerodynamics of vertical-axis wind turbines in full-scale and laboratory-scale experiments

Within a wind farm, multiple turbine wakes can interact and have a substantial effect on the overall power production. This makes an understanding of the wake recovery process critically important to optimizing wind farm efficiency. Vertical-axis wind turbines (VAWTs) exhibit features that are amenable to dramatically improving this efficiency. However, the physics of the flow around VAWTs is not well understood, especially as it pertains to wake interactions, and it is the goal of this thesis to partially fill this void. This objective is approached from two broadly different perspectives: a low-order view of wind farm aerodynamics, and a detailed experimental analysis of the VAWT wake.

One of the contributions of this thesis is the development of a semi-empirical model of wind farm aerodynamics, known as the LRB model, that is able to predict turbine array configurations to leading order accuracy. Another contribution is the characterization of the VAWT wake as a function of turbine solidity. It was found that three distinct regions of flow exist in the VAWT wake: (1) the near wake, where periodic blade shedding of vorticity dominates; (2) a transition region, where growth of a shear-layer instability occurs; (3) the far wake, where bluff-body oscillations dominate. The wake transition can be predicted using a new parameter, the dynamic solidity, which establishes a quantitative connection between the wake of a VAWT and that of a circular cylinder. The results provide insight into the mechanism of the VAWT wake recovery and the potential means to control it.

Minimum drag profiles in infinite cavity flows

The problem considered is that of minimizing the drag of a symmetric plate in infinite cavity flow under the constraints of fixed arclength and fixed chord. The flow is assumed to be steady, irrotational, and incompressible. The effects of gravity and viscosity are ignored.

Using complex variables, expressions for the drag, arclength, and chord, are derived in terms of two hodograph variables, Γ (the logarithm of the speed) and β (the flow angle), and two real parameters, a magnification factor and a parameter which determines how much of the plate is a free-streamline.

Two methods are employed for optimization:

(1) The parameter method. Γ and β are expanded in finite orthogonal series of N terms. Optimization is performed with respect to the N coefficients in these series and the magnification and free-streamline parameters. This method is carried out for the case N = 1 and minimum drag profiles and drag coefficients are found for all values of the ratio of arclength to chord.

(2) The variational method. A variational calculus method for minimizing integral functionals of a function and its finite Hilbert transform is introduced, This method is applied to functionals of quadratic form and a necessary condition for the existence of a minimum solution is derived. The variational method is applied to the minimum drag problem and a nonlinear integral equation is derived but not solved.

Seis passeios pelas praias de uma ficção: notas sobre algumas movimentações de drag queens na cidade do Rio de Janeiro

O presente trabalho tem por objetivo traçar breves notas sobre algumas movimentações de drag queens e outras artistas da travestilidade que tiveram lugar na cidade do Rio de Janeiro, nos anos de 2009 e 2010. Através de um trabalho de observação participante, foram selecionados alguns locais e espetáculos que poderiam ser representativos desta categoria artística, não se pretendendo um levantamento extenso sobre quem são e onde estão tais artistas. Nomeio como artistas da travestilidade aqueles corpos que têm o ato de travestir-se como central em sua construção artístico-cultural, principalmente construindo corporalidades baseadas em um gênero diferente daquele identificado socialmente no nascimento, como drag queens, atores transformistas, travestis e transexuais artistas. Apoiando-me em pressupostos dos métodos cartográfico e etnográfico assumi, nesta dissertação, o posicionamento de um pesquisador-espectador, objetivando o contato com aquilo que drag queens e outras artistas da travestilidade desejam tornar público, ou seja, seus shows e espetáculos. Acompanhei diversas apresentações deste tipo em teatros, boates, bares e clubes de bairro, bem como em outros locais nos quais se fizeram presentes, como na Parada do Orgulho LGBT do Rio de Janeiro e em alguns blocos do carnaval carioca. Tendo ainda como campo de diálogo alguns postulados da Esquizoanálise vertente teórica fundamentada principalmente nas contribuições de Gilles Deleuze e Félix Guattari , pretendi situar e afirmar as drag queens e a arte da travestilidade dentro dos estudos de gênero e sexualidade, principalmente aqueles mais diretamente relacionados às manifestações de uma subcultura camp e cultura gay e/ou homossexual.

Quantification of drag and lift imposed by pop-up satellite archival tags and estimation of the metabolic cost to cownose rays (Rhinoptera bonasus)

The recent development of the pop-up satellite archival tag (PSAT) has allowed the collection of information on a tagged animal, such as geolocation, pressure (depth), and ambient water temperature. The success of early studies, where PSATs were used on pelagic fishes, has spurred increasing interest in the use of these tags on a large variety of species and age groups. However, some species and age groups may not be suitable candidates for carrying a PSAT because of the relatively large size of the tag and the consequent energy cost to the study animal. We examined potential energetic costs to carrying a tag for the cownose ray (Rhinoptera bonasus). Two forces act on an animal tagged with a PSAT: lift from the PSATs buoyancy and drag as the tag is moved through the water column. In a freshwater flume, a spring scale measured the total force exerted by a PSAT at flume velocities from 0.00 to 0.60 m/s. By measuring the angle of deflection of the PSAT at each velocity, we separated total force into its constituent forces — lift and drag. The power required to carry a PSAT horizontally through the water was then calculated from the drag force and velocity. Using published metabolic rates, we calculated the power for a ray of a given size to swim at a specified velocity (i.e., its swimming power). For each velocity, the power required to carry a PSAT was compared to the swimming power expressed as a percentage, %TAX (Tag Altered eXertion). A %TAX greater than 5% was felt to be energetically significant. Our analysis indicated that a ray larger than 14.8 kg can carry a PSAT without exceeding this criterion. This method of estimating swimming power can be applied to other species and would allow a researcher to decide the suitability of a given study animal for tagging with a PSAT.