Active flow control using steady and pulsed blowing at subsonic speeds

An experimental study has been performed on a NASA 17% thick supercritical aerofoil modified with a Coanda trailing edge. The effects of pulsed blowing on aerofoil performance and boundary-layer flow characteristics have been investigated at a Reynolds number of approximately 2.6×105 based on the aerofoil chord to further gain knowledge of the flow physics associated with unsteady circulation control. Various pulsing frequencies have been studied at different angles-of-attack. In order to characterize the flow field around the suction surface of the aerofoil, boundary layer profiles have been measured along the mid-span. In order to relate the changes in the boundary-layer properties to aerofoil performance, force measurements have also been performed using a three-component balance for a range of angles of attack from -20 degrees to +20 degrees. The higher pulse jet, from the range of frequencies tested, provides higher mean-velocity increments at circumferential angles around the Coanda trailing edge up to 30° from the blowing slot. Above 45°, lower pulse frequencies provide higher mean-velocity increments. The force-balance results show that lift is improved as the frequency of pulsed blowing is reduced. Copyright © 2008 by N. Shah, C. Wong, K. Kontis.