An investigation is made of the effect of an artificial baffle introduced in Finite Element modeling of acoustic radiation from turbofan inlets. The purpose of the baffle is to limit the extent of the computational domain in order to maximize the efficiency of the scheme. However, the possibility exists that the baffle, if improperly oriented, will generate spurious reflections which interfere with the true radiated acoustic field. A generic example of a turbofan inlet, including typical geometry and non-uniform potential flow in and around the nacelle, is modeled with a baffle as typically introduced limiting the angular extent of the domain around the inlet to approximately 140 degrees from the inlet axis, and with the baffle removed with the domain of computation being the entire half space surrounding the nacelle. Acoustic modes introduced at the source plane are chosen to produce radiated fields with peak directivity at increasing angles from the inlet axis. Acoustic fields are computed using the baffled and unbaffled models and comparisons made of the baffled results with the baseline unbaffled results. It is found that even with radiation patterns with significant lobes at as high as 70 degrees from the inlet axis very little effect of the baffle on radiation directivity is observed except near the baffle. The effect of the baffle on phase accuracy is tested by representing the noise source with multiple radial modes which produce characteristic multiple lobe radiation patterns due to constructive and destructive interference. The baffle is observed to have little effect on radiation directivity except near the baffle, even when significant lobes are present at angles from the axis as high as 70 degrees, suggesting that both amplitude and phase are not significantly affected by the baffle.


Mechanical and Aerospace Engineering

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Article - Conference proceedings

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Publication Date

01 Jan 1998