Dynamic stall control by leading edge vortex generators

A new concept of passive dynamic-stall control was developed and tested on an OA 209 rotorcraft airfoil during two wind-tunnel test campaigns in 2004 and 2005. 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. Detailed analysis of the flow field by particle image velocimetry and infrared thermography show that this is achieved by a disturbance of the dynamic-stall vortex and therefore separation is partially prevented.