Jet noise shielding provided by a hybrid wing body aircraft

Abstract

One approach toward achieving NASA's aggressive N+2 noise goal of 42 EPNdB cumulative margin below Stage 4 is through the use of novel vehicle configurations like the hybrid wing body. Jet noise measurements from a hybrid wing body acoustic test in the NASA Langley 14-by 22-Foot Subsonic Tunnel are described. Two dual-stream, heated Compact Jet Engine Simulator units are mounted underneath the inverted hybrid wing body model on a traversable support to permit measurement of varying levels of shielding provided by the fuselage. Both an axisymmetric and low noise chevron nozzle set are investigated in the context of shielding. The unshielded chevron nozzle set shows 1-2 dB of source noise reduction (relative to the unshielded axisymmetric nozzle set) with some penalties at higher frequencies. Shielding of the axisymmetric nozzles shows up to 6.5 dB of reduction at high frequency. The combination of shielding and low noise chevrons shows benefits beyond the expected additive benefits of the two, up to 10 dB, due to the effective migration of the jet source peak noise location upstream for increased shielding effectiveness. Jet noise source maps from phased array results processed with the deconvolution approach for the mapping of acoustic sources algorithm reinforce these observations.

Noise measurements of a low-noise top-mounted propulsion installation for a supersonic airliner

“…Based on this, NASA has explored the noise reduction that could be obtained by moving the outboard propulsion to the top of the concept vehicle, estimating the possible acoustic advantages and aerodynamic impacts on range and sonic boom. The results were promising, greatly reducing jet mixing noise and removing fan noise as a contributor to certification noise, much as has been found in previous studies of subsonic aircraft 4,5 . The aerodynamic penalties for top-mounted propulsion are still significant, hence every effort must be made to maximize the noise benefits of this installation.…”