The fan of a turbojet is one of the dominant sources of the noise generated by aircraft in the take-off and approach phases. Consequently, predicting fan noise with a view to reducing it has become a priority research topic.
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numerical simulation of the effects of installation for a nozzle installed above the tail plane in take-off conditions: instantaneous disturbed pressure maps. SabrinA software [DSNA]
This problem is tackled in several current national and European projects that aim to characterize the acoustic shielding effects potentially offered by unconventional aircraft architectures. To this end, Onera has already carried out several experimental and numerical studies with the aim of characterizing the shielding effect that a tail plane might have on the "downstream" fan noise of a dual flow nozzle.
The numerical studies were performed using the sAbrinA calculation software, which can simulate the complex phenomena of acoustic generation and propagation. In 2007, calculations were performed for a nozzle configuration installed above a tail plane fin profile, on the one hand, idle and, on the other, in flow conditions representative of a take-off. The figures below present some results, in which we can clearly distinguish the shielding effect of the profile on the acoustic radiation.
Authors: Stéphane Redonnet and Guillaume Desquesnes, researchers in aeroacoustics at Onera (DSNA).
The acoustic shielding effect due to the tail plane is shown up by the attenuation
of waves on the profile's under surface and their reinforcement on the upper surface. [static state, on the left; take-off state, on the right]
View of the acoustic propagation in the median plane of the nozzle [static state, on the left; take-off state, on the right]