Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace Engineering Sciences

First Advisor

Lucy Y. Pao

Second Advisor

Robert R. McLeod

Third Advisor

Kurt Maute

Fourth Advisor

Patrick Moriarty

Fifth Advisor

Andrew Clifton

Abstract

Ice accumulation on wind turbines operating in cold regions reduces power generation by degrading aerodynamic efficiency and causes mass imbalance and fatigue loads on the blades. Due to blade rotation and variation of the pitch angle, different locations on the blade experience large variations of Reynolds number, Nusselt number, heat loss, and non-uniform ice distribution. Hence, applying different amounts of heat flux in different blade locations can provide more effective de-icing for the same total power consumption. This large variation of required heat flux motivates using distributed resistive heating, with the capability of locally adjusting thermal power as a function of location on the blade. The main contributions of this research are developing the experimental feasibility of direct ice sensing using an optical sensing technique as well as development of a computational framework for implementation of closed-loop localized active de-icing using distributed sensing. A script-base module was developed in a commercial finite-element software (ANSYS) which provides the capability of (i) Closed-loop de-icing simulations for a distributed network of sensors and actuators, (ii) investigating different closed-loop thermal control schemes and their de-icing efficiency (iii) optimizing thermal actuation for a distributed resistive heating, and (iv) analyzing different faulty scenarios for sensors and thermal actuators under known faults in the network. Different surrogate models were used to enhance the computational efficiency of this approach. The results showed that optimal value of control parameters in a distributed network of heaters depends on convective heat transfer characteristics, layout of heaters and type of closed-loop controller scheme used for thermal actuation. Furthermore, It was shown that closed-loop control provides much faster de-icing than the open-loop constant heat flux thermal actuation. It was observed both experimentally and numerically that high intensity pulsed thermal actuation slightly improves ice melting but relatively increases the amount of applied thermal stress to the blade structure. This thesis includes: (1) A literature study on different methods of ice detection and a review on passive and active anti/de-icing techniques on wind turbines, (2) Development of an optical ice sensing method for direct detection of ice on the blade including experimental results, (3) Description of an aero/thermodynamic model, which predicts how much heat flux is needed locally for de-icing under variable atmospheric conditions, (4) Experimental results showing the proof-of-concept of closed-loop de-icing using distributed optical ice sensing, distributed temperature sensing, and resistive heating, and (5) Numerical modeling of ice melting on a blade for different distributed heater layouts and geometries in order to optimize thermal actuation strategy, improve de-icing efficiency, and finally (6) Development of a computational framework for closed-loop active de-icing using distributed localized heating and sensing.

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