The Distribution of Pressure on an Aerofoil, in a Stream with a Spanwise Velocity Gradient

Summary

Pressure measurements were made at one section of an aerofoil of constant chord spanning a wind tunnel. A flat plate was mounted in the tunnel upstream of the aerofoil, so that the wake from the plate produced a spanwise velocity gradient at the aerofoil. By traversing the plate across the tunnel the position of the wake could be altered relative to the pressure holes in the aerofoil, so that the complete pressure distribution over the aerofoil in the neighbourhood of the wake could be found. The results showed that, because of the secondary flow produced by the interaction between the aerofoil and the wake, the variation of pressure across the wake for a given chordwise position was very small, except close to the leading edge. Thus the lift coefficient, based on the velocity outside the wake, was nearly constant across the wake. The form drag coefficient, based on the same velocity, was considerably reduced in the wake. Even when the form drag coefficient was based on the local velocity of the stream, a considerable reduction was found in the wake.