Rotary Wing CLFC · Closed-Loop Flow Control to Enhance Aerodynamic and Aeroacoustic Performance of Wind-Turbine Blades

Closed-Loop Flow Control to Enhance Aerodynamic and Aeroacoustic Performance of Wind-Turbine Blades

Aerodynamic loads and noise emitted by rotating blades are of interest in many industrial applications, such as wind-turbines, aircraft propellers, and helicopter blades. The focus of the Rotary-Wing CLFC project is harvesting of wind-energy while reducing negative environmental impact. These double aims are important given that it is crucial to increase energy harvesting from the environment without producing more green-house gases. To achieve the latter, we have to improve our understanding of the contributing processes. Wind-turbines should be designed such that they have a low impact on the environment and on society. Additionally, to reduce the impact on inhabited areas, their noise emission should be low. Similar arguments hold for aircraft propellers and helicopter blades as well. Wind-turbine blades operate under a highly turbulent atmospheric boundary layer where they encounter gusts and variation in wind direction and speed. These decidedly changeable harsh conditions affect both aerodynamic and aeroacoustic performance. The aerodynamic noise is, in fact, a result of interaction between the turbulent flow and the blade; accordingly, flow unsteadiness and noise interact strongly. For this reason, the Rotary-Wing CLFC project aimed to achieve a combined aerodynamic and aeroacoustic optimization of the rotary wing by experiments conducted in a controlled environment of gusting flow and rotating motion. The first objective was to develop an aero-acoustic model that could be incorporated in a control strategy. The second objective was directly aimed at the development of strategies for the reduction of blade noise. The third key technological objective was to develop a control system. The last objective was to investigate the effect of rotation. The investigations carried under the Rotary-Wing CLFC project focused on wind-turbine applications. To impact a large flow region, so-called active flow control technology in the form of wall normal blowing was chosen. Using this technique, dynamic processes in the flow are excited by boundary actuation, exploiting amplification effects due to flow instability so that results can be obtained with a minimal amount of input energy. Moreover, passive flow control technologies were developed to enhance the amount of energy harvested from the wind, while improving the aero-acoustic properties. Passive methods benefit from a simple and robust design. Leading- and trailing-edge serration were proven to be effective in reducing the noise emitted from wind-turbine blades. The leading-edge region of the wind turbine blade was modified to incorporate leading-edge serrations and active flow control in the form of wall normal blowing.

Data: CORDIS, © European Union