Semester

Summer

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

James Smith

Abstract

There are currently millions of people throughout the world who live in isolated, rural communities without electricity. An ongoing effort has been initiated to provide reliable power to such communities. These efforts are being made to utilize renewable energy sources such as wind and solar power to solve this problem. Renewable energy sources can be both intermittent and unpredictable. Thus, an effective energy storage system is sought to store excess energy when available to disperse during times of scarcity.;The use of a high-inertia flywheel was proposed as a means of energy storage due to its simplicity, low cost, and reliability. A previously proposed design integrated a flywheel with a windmill and grid system to effectively distribute consistent power for a village of approximately 200 residents. The flywheel was designed to store enough energy for the residents for up to two days without input. The proposed design consists of a cylindrical flywheel with a diameter of 5.9 meters, a thickness of almost 0.9 meters, and a mass of 152 tons. A rotating disk with these proportions creates a large amount of parasitic drag at its maximum angular velocity. The amount of drag created causes major losses to the overall power output of the wind energy storage system.;Parasitic drag is predominantly caused by the skin friction an object moving through a viscous fluid experiences. This skin friction is strongly influenced by the viscosity of the surrounding fluid. Viscosity is a function of pressure and temperature and can be greatly reduced as the atmospheric pressure surrounding the concerned object is lowered. A drag analysis was completed to assess the benefits of reducing the air pressure within the chamber created between the flywheel and its enclosing walls. It was found that placing the flywheel within a housing alone reduces the frictional losses by approximately 15 percent; this reduction is governed by proper spacing based on boundary layer interactions. As the chamber pressure is reduced, the friction moment of the flywheel can be diminished even further. It was found that at one-twentieth of an atmosphere, the parasitic drag was reduced by an additional 80 percent. Several design methods are considered in order to reduce the pressure around the flywheel to a target of 1/20 of an atmosphere. With the help of a reduced pressure chamber tightly fit around the flywheel, the overall viscous torque of the flywheel can be reduced by over ninety percent when compared to the same flywheel operating in free space at atmospheric conditions. Using CFD methods (FLUENT) as a simulated design tool, the optimum gap spacing for the housing was analyzed; a variety of casing geometries were considered in an attempt to determine optimal clearance. A central low pressure drag reduction system can be created by enclosing the rotating flywheel, leaving an optimal spacing of 0.0826 meters in the axial direction and 0.0826 meters in the radial direction (optimization based on comparison between specific geometries modeled using FLUENT) using a vacuum pump to evacuate the region between the spinning flywheel and stationary housing down to a target of 1/20 of an atmosphere.

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