Wind turbine power curve optimization via Active Flow Control
One of the greatest challenges of our society is to improve the efficiency of energy-converting devices, as well as to advance in the use of clean, low-cost renewable energy. In this project, we focus on the wind energy generated by large horizontal axis wind turbines (HAWT). The objective is to develop novel techniques to improve their performance and operating range, affecting the intermittency of these systems and the cost of the energy generated. In particular, this project will tackle two of the main limitations of wind turbine designs:
Wind turbine blades experience low-span flow separation in production: This aspect is especially relevant between the cut-in and rated wind speeds, where the blade loading is not especially high, and suppression of flow separation by means of, e.g., active flow control (AFC) devices, as proposed in this project, may result in an increase of the torque, and thus in the produced energy. This could be seen as an enhancement of the turbine performance.
The pitch control overloads the inboard part of the blades beyond the rated speed: Due to the correlation that the pitch mechanism imposes to all blade sections, the tangential loads have to be significantly increased to keep the maximum torque. In this project, we propose the combination of pitch actuation with selective promotion of flow separation beyond the rated speed, to break locally the correlation of the blade sections. In particular, 1) flow separation would be intentionally promoted in selected blade regions to reduce the loads where necessary, and 2) the pitch settings would be re-tuned to meet the maximum torque, while ensuring that the loads in all the blade sections do not exceed the design specifications.
Together with the mentioned increase in turbine performance below the rated speed and the load alleviation capabilities represented by these two objectives, the correct management of flow separation within the whole turbine operating range would also allow to:
Reduce the cut-in wind speed: As suppression of the low-span flow separation increases the rotor torque, power generation by the turbine is thus expected to start at lower wind speeds.
Increase the cut-out wind speed: Flow separation in selected blade sections is expected to result in a more effective blade loading control strategy. This would allow extending the wind turbine operating range beyond the cut-out speed of the baseline turbine design.