AbstractsEngineering

Experiments have been made on a thin, two-dimensional aerofoil with sharp leading edge and with a jet blowing through a mid-chord slot on the upper surface for boundary-layer and circulation control.The measurements were made at low Mach number and included the effect of altering the angle of blowing for it was anticipated that this would help control the leading edge separation bubble.It was found that variation of the blowing angle caused very little change in lift coefficient but produced an appreciable change in moment coefficient. With the jet discharging at an angle and subsequently reattaching to the surface a separation bubble of low pressure was formed downstream of the slot which reduced the nose-up pitching moment about the guarter-chord point. The reattachment distances for this bubble have been successfully predicted by an extension of the Bourque-Newman theory for reattaching jets. The lift and moment coefficients before the stall were compared with Spence's jet flap theory which has been extended within the context of thin aerofoil theory, to include the effect of jet entrainment. It is predicted that the entrainment tends to increase the lift by increasing the effective camber of the aerofoil and the detailed agreement between this theory and experiment is good.