Author's School

School of Engineering & Applied Science

Author's Department/Program

Mechanical Engineering and Materials Science

Language

English (en)

Date of Award

1-1-2011

Degree Type

Thesis

Degree Name

Master of Arts (MA)

Chair and Committee

Ramesh Agarwal

Abstract

In recent years, it has been theoretically suggested by some researchers that the power coefficient of a wind turbine can be increased beyond the Betz limit for a bare turbine by enclosing the turbine with a duct. In this thesis, this potential for increases in power generation by adding a shroud around a turbine is investigated using numerical flow modeling. Two configurations for ducted turbines are considered for numerical simulations and optimization. The first configuration considers shrouds for standard horizontal axis wind turbines. Several turbine diameters, wind speeds, and shroud sizes are considered. The results show that shrouding can almost double the power that would be generated by a bare turbine. The second configuration considers the potential of converting abandoned or unused farm silos into solar chimneys with low cost shape modification of the chimney to further augment the power generation. The most effective, simple and low cost shape modification is found to be a diffuser added to the top of the silo, which can increase the power output by nearly 50%. Increasing the buoyancy effect by heating the air at the base of the silo can further increase the power output by a significant amount, as much as 50%. It should be noted that in this configuration, the effect of cross flow wind at the exit of the diffuser can have a negative effect on the generated wind power; however, it is surmised to be small. Both these configurations are analyzed by employing computational fluid dynamics flow solver, which solves the Reynolds-Averaged Navier-Stokes equations, in conjunction with a two equation k-epsilon turbulence model. The turbine is modeled as an actuator disk neglecting the rotational effects. The diffuser shapes in both the configurations are optimized using a genetic algorithm. The computations show that the shrouded turbines can generate greater power than that generated by the bare turbines and should be considered for small and medium size turbines. Further investigation is needed in the overall economic benefit considering the initial investment, maintenance and life cycle costs. The technical feasibility of shrouding a turbine and the structural integrity of a shrouded turbine are also major considerations.

Comments

Permanent URL: http://dx.doi.org/10.7936/K7PV6HFC

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