A Further Wind Tunnel Investigation of Underwing Jet Interference bY

SUMMARY Further experiments, to investigate the interference of the Jet stream issuing from a high bypass ratio engine mounted below a wing, are described. Tests have been made with a two-dimensional wing, and two nozzle shapes representing engues with different fan cowl lengths. A Jet blonng from these nozzles produced negligible interference on the wing upper surface. However, a change in th8 lower surface pressure distribution occurred which was dependent only on the wing and nozzle geometry. This interference was dominated by a high suction peak, which appeared to be related to a region in the Jet where the alternate expansion and compression waves were not uniformly spaced. The tests were conducted mostly without an engine pylon. When a pylon was introduced the effect was reduced slightly, but the character of the Interference remained unaltered. An attempt was made to show the possibility of a wing altering the noise level by reflecting the sound from a Jet. Sohlieren pictures were taken with a spark source, but the expected phenomenon of aero-acoustic resonance was not found.