UBC Theses and Dissertations
On the performance and wake aerodynamics of the Savonius wind turbine Fernando, Mahamarakkalage Saman Udaya Kumar
The objective of the thesis is to establish methodology for development of a wind turbine, simple in design and easy to maintain, for possible application in developing countries. To that end the Savonius configuration is analyzed in detail both experimentally and analytically to lay a sound foundation for its performance evaluation. Following a brief review of relevant significant contributions in the field (Chapter I), an extensive wind tunnel test-program using scale models is described which assesses the relative influence of system parameters such as blade geometry, gap-size, overlap, aspect ratio, Reynolds number, blockage, etc., on the rotor output. The parametric study leads to an optimum configuration with an increase in efficiency by around 100% compared to the reported efficiency of ≈ 12 — 15%. Of particular interest is the blockage correction procedure which is vital for application of the wind tunnel results to a prototype design, and facilitates comparison of data obtained by investigators using different models and test facilities. With the design and performance results in hand, Chapters III — VI focus attention on analytical approaches to complement the test procedure. Using the concept of a central vortex, substantiated by a flow visualization study, Chapter III develops a semi-empirical approach to predict the rotor performance using measured stationary blade pressure data. The objective here is to provide a simple yet reliable design tool which can replace dynamical testing with a significant saving in time, effort, and cost. The simple approach promises to be quite effective in predicting the rotor performance, even in the presence of blockage, and should prove useful at least in the preliminary design stages. Chapter IV describes in detail a relatively more sophisticated and rigorous Boundary Element Approach using the Discrete Vortex Model. The method attempts to represent the complex unsteady flow field with separating shear layers in a realistic fashion consistent with the available computational tools. Important steps in the numerical analysis of this challenging problem are discussed at some length in Chapter V and a performance evaluation algorithm established. Of considerable importance is the effect of computational parameters such as number of elements representing the rotor blade, time-step size, location of the nascent vortices, etc., on the accuracy of results and the associated cost. Results obtained using the Discrete Vortex Model are presented and discussed in Chapter VI, for both stationary as well as rotating Savonius configurations. A detailed parametric study provides fundamental information concerning the starting and dynamic torque time histories, power coefficient, evolution of the wake, Strouhal number, etc. A comparison with the flow visualization and wind tunnel test data (Chapter II) shows remarkable correlation suggesting considerable promise for the approach. The thesis ends with concluding remarks and a few suggestions concerning possible future research in the area.