Summary

The present work accounts for the development of an experimental bench for jet noise testing which was used for the analysis of installation effects from jet flows issued by nozzles with and without chevrons. After a verification process of the flow and noise data generated from the bench, investigations were carried out in order to study the physical mechanisms affecting the noise from jets in the vicinity of a flat plate representing the installation of a wing. Particularly, the analysis is made from jet-over-wing mounting configurations for which it was investigated the influence of chevrons on the jet-surface noise and on the shielding effect. For nozzle-to-surface weakly coupled configurations, the results revealed that chevrons, which are generally beneficial for noise attenuation in isolated jets, also interfere in the sound diffraction and scattering generated by the surface on the flow-related sound sources, leading to noise reductions of installed jet configurations. On the other hand, for nozzle-to-surface highly coupled configurations, the acoustic benefits of chevrons were significantly decreased. That observation is related to a higher jet spreading for the chevron nozzle and then a larger area covered by flow, intensifying the jet-surface noise, so that in the critical case, the chevron nozzle issued noise levels higher than the baseline nozzle. Moreover, hot-wire anemometry measurements of the flow field of installed jets were conducted for the cases that presented the largest differences in the noise spectrum in comparison to the isolated jet configuration. This methodology made it possible to identify the main mechanisms responsible for the modifications observed in acoustic far-field. Finally, a parametric study was carried out to correlate the overall sound pressure level with the jet flow characteristics and plate position, seeking a reasoning to identify silent installed configurations.

Material for download