| A fast, efficient way to control loads on industrial scale turbines is important for the growth of the wind industry. Active Aerodynamic Load Control (AALC) is one area which addresses this need. In particular, microjets, which are pneumatic jets located at the trailing edge of a wind turbine blade and blow perpendicular to the blade surface, are a possible AALC candidate. First, the Computational Fluid Dynamics (CFD) solver OVERFLOW is used to explore the effects of a microjet on lift, drag, and pitching moment. Then the interaction between an aerodynamic disturbance and an airfoil equipped with a microjet is modeled. The object of this dissertation is to investigate microtabs as viable AALC devices by presenting their aerodynamic properties and testing whether a proportional-integral (PI) controlled jets can alleviate loads caused by wind gusts. The use of CFD to simulate a microjet is validated by comparing the results to both previous experiments found in the literature as well as wind tunnel tests completed at UC Davis. The aerodynamic effectiveness of the jet is investigated as a function of various parameters such as Reynolds number, angle of attack, and the momentum coefficient of the jet. The effects of the microjet are found to be very similar to another AALC device, the microtab. An aerodynamic disturbance is simulated, and a control algorithm which is incorporated into the OVERFLOW code is used to activate the microjet, thus reducing the change of the blade load due to the gust. Finally, a more realistic model is made by adding both a linear and a torsional spring and damper to represent the blade movement. This two-degree of freedom system shows that during a gust the vertical blade movement is reduced when the microjets are activated. Microjets are found to work well to alleviate the changes in aerodynamic loads felt by the airfoil, and are therefore a good candidate for a practical AALC device. However, further investigation is needed in the areas of aeroacoustics, system energy requirements, and logistics of implementation. |
