Some notes on the flow patterns observed over various swept-back wings at low Mach numbers (in the R.A.E. 10-ft x 7-ft high speed tunnel)

Abstract

This paper collects together the flow patterns observed by an oil film (titanium oxide) technique over ten different Swept-back wings at high incidence and low Mach number in the Royal Aircraft Establishment 10-ft X 7-ft High Speed Tunnel. The designs range from 0.04 to 0.10 in mean thickness/chord ratio and from 40 deg to 60 deg in angle of sweep. Almost all the wings suffer from a leading-edge separation and the paper discusses in general terms how the regions of flow separation, together with their associated part-span vortex sheets are affected by changes in incidence, Reynolds number and wing design. Some brief reference is made to how the flow patterns are related to the overall force and moment characteristics and how these characteristics might be improved by the use of different types of modification. It appears that some correlation may ultimately be established between the spanwise extent of the separation over a swept-back wing at a given incidence with concepts based on two-dimensional flow and the pressure distribution over the swept wing in polential flow. No correlation can be expected in terms of the chordwise extent of the separation, in view of the presence of 'part-span vortex sheets'. The need for research into the 'bursting' of 'short' separation bubbles in two-dimensional flow and into the nature and reasons for the part-span vortex sheets in three-dimensional flow is especially emphasized.