Date of Award

2020

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Fernando Ponta

Committee Member 1

Leonard Bohmann

Committee Member 2

Sajjad Bigham

Committee Member 3

Hassan Masoud

Abstract

Wind, by its vary nature, varies with place and time, making energy conversion diffi- cult. This calls for the development of improved technologies that efficiently harness energy from the available wind resource, and advanced control systems are a key re- search aspect of wind turbine technology. Such systems are needed to maximize the rotor’s output power at wind speeds below the nominal value for the turbine, limit rotor power at wind speeds higher than the nominal, and reduce fluctuating loads on the turbine blades that may compromise their long-term operational life. Among the several families of control methods for wind turbines, Pitch and Stall are by far the most used in modern utility-scale machines. Both are based on altering the aerody- namic characteristics of the blade sections in order to control the forces which produce the rotor’s torque, power, and thrust, and its deformation. A very popular control method to optimize power production and control is using Variable- Speed Wind Turbines (VSWT) a relatively new idea, which offers has a promising perspective for future applications. As with the classical Fixed-Speed (FS) stall method lowers the capital cost and reduces maintenance expenses, while at the same time, allows for a more efficient and precise control of power production. This research investigated the aeroselastic behavior of the stall-controlled rotors, studied the frequency content and time evolution of their oscillatory behavior, and gained a better understanding of

the underlying physics. This calls for a wide range of experiments that assess the ef- fects of rapid variations on the rotor’s operational conditions, like gusts and turbulent fluctuations on the wind flow. To systematize this analysis, various gust conditions tested for different wind speeds. These are represented by pulses of different intensity, occurring suddenly in and otherwise constant wind regime. This allows us to observe the pure aero-elasto-inertial dynamics of the rotor’s response. We will show the re- sults from an extensive series of experiments analyzing the aeroelastic response of the rotor to wind speed fluctuations associated to the turbulent characteristics of the atmospheric boundary layer, focusing on obtaining a reduced-order characterization of the rotor’s dynamics as an oscillatory system based on energy-transfer principles. Besides on its intrinsic scientific value, this aspect of the work presented here is of fundamental interest for researchers and engineers working on developing optimized control strategies for wind turbines. It allows for the critical elements of the rotor’s dynamic behavior to be described as a reduced-order model that can be solved in real-time, an essential requirement for determining predictive control actions.

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