Este documento resume el desarrollo de las herramientas computacionales inflow, basadas en el método de elementos finitos, para la solución de problemas de mecánica de fluidos bi-dimensionales bajo régimen de flujo incompresible. Se desarrollan algoritmos de solución de las ecuaciones de Navier-Stokes incompresibles, que podrán ser utilizados para fines de desarrollo o investigación. Se implementó un paquete básico de herramientas computacionales, bajo una lógica de programación modular, sobre el cual se podrán ir anexando subrutinas para solucionar otras condiciones de flujo (otros mode-los de turbulencia, el caso de flujos con rotación, estabilización para casos de rotación domi-nante, flujos debidos a gradientes térmicos, etc.). Aunque las funciones elementales que se han programado corresponden a elementos bidi-mensionales, las subrutinas de ensamble y solución se implementaron teniendo en cuenta el caso más general tridimensional, con lo que la extensión al mismo resulta directa.

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Available from: Julio Massa, Jan 26, 2015
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    ABSTRACT: Design tools have been developed for ultra-low Reynolds number rotors, combining enhanced actuator-ring / blade-element theory with airfoil section data based on two-dimensional Navier-Stokes calculations. This performance prediction method is coupled with an optimizer for both design and analysis applications. Performance predictions from these tools have been compared with three-dimensional Navier Stokes analyses and experimental data for a 2.5 cm diameter rotor with chord Reynolds numbers below 10,000. Comparisons among the analyses and experimental data show reasonable agreement both in the global thrust and power required, but the spanwise distributions of these quantities exhibit significant deviations. The study also reveals that three-dimensional and rotational effects significantly change local airfoil section performance. The magnitude of this issue, unique to this operating regime, may limit the applicability of blade-element type methods for detailed rotor design at ultra-low Reynolds numbers, but these methods are still useful for evaluating concept feasibility and rapidly generating initial designs for further analysis and optimization using more advanced tools.
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    ABSTRACT: Wake development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low-speed wind tunnel. Standard hot-wire techniques were used to study the velocity fluctuations. The Reynolds number range of periodic vortex shedding is divided into two distinct subranges. At R=40 to 150, called the stable range, regular vortex streets are formed and no turbulent motion is developed. The range R=150 to 300 is a transition range to a regime called the irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent transition in the free layers which spring from the separation points on the cylinder. This transition first occurs in the range R = 150 to 300. Spectrum and statistical measurements were made to study the velocity fluctuations. In the stable range the vortices decay by viscous diffusion. In the irregular range the diffusion is turbulent and the wake becomes fully turbulent in 40 to 50 diameters downstream. It was found that in the stable range the vortex street has a periodic spanwise structure. The dependence of shedding frequency on velocity was successfully used to measure flow velocity. Measurements in the wake of a ring showed that an annular vortex street is developed.
  • seventh 01/1979; McGraw-Hill.
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