Low-speed-tunnel model tests on the flow structure behind a delta-wing aircraft and a 40 deg swept-wing aircraft at high incidences

Abstract

In view of the possibility of trimming some swept-wing aircraft at incidences above the stall, there has been a desire to visualise the whole pattern of vortex sheets and separated flow starting from the stalling wing, and to follow it back beyond the tailplane. To supplement other methods, a swivelling head has been used, giving the velocity, pitch and yaw, and results are given in this report for a 48-deg delta (Javelin) and a 40-deg swept-wing aircraft (Swift without fences). The tests showed that at incidences beyond the stall there is a large bubble of separated flow behind the wing. For the delta at 35 deg this bubble had not closed at the station of the tailplane and extended over the whole of the region behind the wing. The velocity and pressure field found in the separated flow resembles that behind a square plate at 90 deg. The vorticity pattern, measured in a plane cutting the bubble of separated flow from the stalled wings, is complicated by rotating masses of air inside the bubbles, between the strong inner vortex sheets, and the weaker tip vortices. The results have been analysed to show the effect of change of tail height.