Blown flap noise research

Abstract

f l a p noise t o the t o t a l a i r c r a f t noise 1s assessed.Noise data were obtained with models of both internally and externally blown jet-flaps of the type currently being developed f o r STOL a i r c r a f t . The principal t e s t s were conducted with an augmentor-wing model and with an externally-blown double-slotted-flap model. Secondary t e s t s were 'D

Externally-blown-flap noise

“…The overall sound pressure level (OASPL) as a function of microphone angle, 6, is given for flap positions of 30°-60°, 10°-20°, and 0° (fully retracted) and for the nozzle alone. As has been noted with the previous small model results (3) there is a large increase in noise below the wing as the flaps are lowered into the nozzle exhaust. For example at 6 = 90° (which would be directly below the airplane) there is a 10 dB increase in noise when the flaps are lowered from the retracted (0°) to the 30°-60° flap position.…”

Externally blown flap impingement noise

“…Static and dynamic pressures were also measured on the undersurface of the wing and those results will be reported in a NAS. 4 technical publication.…”

“…The aft-radiated fan It has been observed in noise tests using cold flow scale models of EBF systerns (2)(3)(4)(5) that the interaction of the rxh:rust flow with the flap system is a significant source of noise. To obtain data on the noise generated by the impingement of turbofan engine exhaust on an aircrzft wing 2nd flap assembly a t full scale, the NASA Flight Research Center set up a ground test facility using R wing with double-slotted flaps and a turbofan engine.…”

Rational Function Representation of Flap Noise Spectra including Correction for Reflection Effects

“…ithout atmospheric attenuatio obtained by including reflection effects with the lossless value of SPL is given by SPL(fc)= SPL+(fc) + 10 log 1 0 IT(fc) 2 (11) where IT(fc) 2 is the reflectance and SPL+(fc) (eq. (1)) is the sound pressure level without atmospheric attenuation and ground reflection.…”

“…For use in the determination of IT(fc)1 2 ' by a computer, the reflected ray transfer function G(s) will be assumed to be independent of frequency. Hence in equation (14), IQ(fc)l and 6 (fc) will be replaced by the constants IQI and 6.…”