Experiments on the Effect of Ground Reflections on Supersonic Jet Noise

The influence of ground reflections on the measurement of aircraft engine exhaust noise is examined in this paper. A series of experiments were performed in the UCI aeroacoustic facility of supersonic jet noise with and without a ground plane in close proximity to the jet. Thus the effect of the ground plane on the radiated noise was isolated. Additionally, a computational model for the phenomenon was developed, which included the determination of a distribution of noise sources within the jet column. This distribution was developed from phased microphone array measurements incorporating an advanced beamforming algorithm. The developed model did a reasonably good job of predicting the effect of the reflecting ground surface. The most important exception is in the additional noise source caused by aerodynamic “scrubbing” of the turbulent jet on the surface far downstream of the jet exit. Guidance on how to alter the proposed model to account for porosity of the ground in field experiments over grassy or sandy terrain, is also given.