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theses

Vertical axis type wind turbines, which offer promising solutions for distributed power generation, have not received adequate attention due to technological drawbacks which need to be addressed. In the present work, a vertical axis drag based turbine is proposed that allows for an improved turbine performance by eliminating recovery stroke losses. This is achieved by optimizing the cyclic drag forces on its blades. The turbine's blades are flat plates; the projected area of which can be drastically varied by varying its pitch angle. To utilize this effect, the turbine blades pitch by 90° between the two turbine strokes manipulating their effective area using a novel cyclic blade pitching mechanism. This passive mechanism orients the blades vertically during the drive stroke for maximum effective area and horizontally during the recovery stroke for minimum effective area with respect to the fluid flow. These blade orientations maximize the positive drive stroke force and minimize the recovery stroke losses to allow for maximum net energy capture and an improved turbine performance. The turbine, owing to its blade movements is called the Cyclic Pitch Turbine (CPT) and its working principle resembles that of an oar blade in the sport of shell rowing.

A theoretical model of the CPT turbine is developed to predict the performance and optimize the turbine parameters and it is validated using wind tunnel and water channel experiments. The turbine is self-starting at all turbine orientations and has a better and more uniform static torque coefficient than the popular Savonius turbine. The dynamic analysis also indicates a higher performance for CPT and the predicted values for torque and power coefficients match very closely with those from water channel and wind tunnel experiments on a fabricated prototype. Optimization of the turbine parameters is performed which clearly shows that, a shorter drive stroke 140° and a tip speed ratio value close to 0.5 results in optimal power generation. Several blade shapes are tested in the wind tunnel and the results indicate that airfoil section blades with long and narrow continuous shapes that have less area towards the blade's tip result in higher performance. This thesis stands as a proof of concept work on cyclic pitch turbines which can be used to efficiently harvest wind energy in residential areas and also hydro-kinetic energy from tides and river streams.

ETD_9255

Ph.D.

Includes bibliographical references

by Jubilee Prasad Rao

doi:10.7282/t3-6v6k-9r32

ETD doctoral

The author owns the copyright to this work.