Flow Control on Helicopter Rotor Blades

Kurzfassung

The main focus of this talk is laid on the work in the field of rotary-wing aircraft during the last 15 years. Emphasis is put on passive and active control technology to face the main problems in modern helicopter design: noise and vibration due to blade-vortex-interaction and dynamic stall. These are not only a drawback to comfort but have a significant impact on the aircrafts structural weight and lifetime. Inspired by humpback whale flippers, in 2004 and 2005 a new concept of passive dynamic-stall control was developed and tested on a rotorcraft airfoil during two wind-tunnel test campaigns. Small vortex generators are mounted at the leading edge of the rotor blade. At low incidence they are located close to the stagnation point and do not impact the flow field. At high angles of attack the so-called leading edge vortex generators (LEVoGs) induce longitudinal vortices which impact the suction side flow. It is shown that the use of LEVoGs can significantly increase the overall time-averaged lift while an unwanted negative pitching-moment peak is reduced compared with the clean-wing case. Furthermore, overall drag is reduced at dynamic-stall conditions. This may reduce fuel consumption, increase comfort or open the possibility to design lighter and more efficient helicopter rotor blades.