Aerodynamics of a rigid curved kite wing

A preliminary numerical study on the aerodynamics of a kite wing for high altitude wind power generators is proposed. Tethered kites are a key element of an innovative wind energy technology, which aims to capture energy from the wind at higher altitudes than conventional wind towers. We present the results obtained from three-dimensional finite volume numerical simulations of the steady air flow past a three-dimensional curved rectangular kite wing (aspect ratio equal to 3.2, Reynolds number equal to 3x10^6). Two angles of incidence -- a standard incidence for the flight of a tethered airfoil (6{\deg}) and an incidence close to the stall (18{\deg}) -- were considered. The simulations were performed by solving the Reynolds Averaged Navier-Stokes flow model using the industrial STAR-CCM+ code. The overall aerodynamic characteristics of the kite wing were determined and compared to the aerodynamic characteristics of the flat rectangular non twisted wing with an identical aspect ratio and section (Clark Y profile). The boundary layer of both the curved and the flat wings was considered to be turbulent throughout. It was observed that the curvature induces only a mild deterioration of the aerodynamics properties. Pressure distributions around different sections along the span are also presented, together with isolines of the average pressure and kinetic energy fields at a few sections across the wing and the wake. Our results indicate that the curvature induces a slower spatial decay of the vorticity in the wake, and in particular, inside the wing tip vortices.Comment: 13 pages, 13 figures. Submitted to "Renewable Energy

Emission features of microstructures fabricated by two-photon polymerization containing three organic dyes

Fabrication of microstructures containing active compounds, such as fluorescent dyes and nanoparticles have been exploited in the last few years, aiming at applications from photonics to biology. Here we fabricate, using two-photon polymerization, microstructures containing the fluorescent dyes Stilbene 420, Disodium Fluorescein and Rhodamine B. The produced microstructures, containing dyes at specific sites, present good structural integrity and a broad fluorescence spectrum, from about 350 nm until 700 nm. Such spectrum can be tuned by using different excitation wavelengths and selecting the excitation position in the microstructure. These results are interesting for designing multi-doped structures, presenting tunable and broad fluorescence spectrum. (C)2012 Optical Society of AmericaFAPESPFAPESPCNPqCNPqCAPES from BrazilCAPES from Brazi

Femtosecond lasers for processing glassy and polymeric materials

Novel materials have been developed to meet the increasing mechanical, electrical and optical properties required for technological applications in different fields of sciences. Among the methods available for modifying and improving materials properties, femtosecond laser processing is a potential approach. Owing to its precise ablation and modification capability, femtosecond laser processing has already been employed in a broad range of materials, including glasses and polymers. When ultrashort laser pulses are focused into a transparent material, the intensity at the focus can become high enough to induce nonlinear optical processes. Here, we report on femtosecond (fs) laser microfabrication in special glasses and polymers. Initially, we describe fs-laser micromachining on the surface of copper doped borate and borosilicate glasses. Subsequently, we present results on two-photon induced polymerization to fabricate microstructures containing fluorescent dyes for manufacturing optical microcavities. Both approaches are promising for designing optical and photonics micro/nanodevices