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Title: Theoretical methods to predict near-field fuselage installation effects due to inlet fan tones
Author: Gaffney, James
ISNI:       0000 0004 6422 250X
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2016
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There are many analytical models to predict turbofan noise radiation in a free field. However, these models explicitly ignore the effect of the aeroplane components on the engine noise. The effects of the aeroplane on the radiated noise must be included because it is the installed engine that affects people in the cabin and community. The original contribution of this thesis is to present a theoretical model for the near-field fuselage installation effects on tonal noise radiating from a turbofan engine inlet. Historically, the fuselage installation effects have been modelled using theoretical methods for open-rotor type sources. Installation effects include the scattering effect from the fuselage, and the refraction effect of the boundary layer running down the fuselage. In this thesis the established techniques are extended to include a new sophisticated analytical source for spinning modes radiating from a circular duct. The source model includes the diffraction effect of the duct lip. The model applies Fourier methods and implements the Wiener-Hopf method for diffraction. Owing to the physics of the problem, simplications in geometry and flow do not curtail the validity of the predictions. The refraction effect was quantified by evaluating the difference between sound pressure levels with and without the boundary layer. Upstream of the source the refraction leads to a paucity of surface acoustic pressure, yet downstream the boundary-layer effect was minimal. Further investigations led to an alternative method of simulating refraction by altering wavenumbers in Fourier space. The installation method was optimised for a turbulent boundary-layer profile by replacing a power-law with a scaled step-change boundary-layer profile. The model developed in this thesis combines the most sophisticated analytic radiation models with current installation models. Due to the speed of the method, the intended purpose for industry is to refine variables via parametric studies. Once these are established, a numerical method could include more complex geometry and flow to the model. By calculating the noise on the outside of the fuselage, the quantity and distribution of acoustic lagging can be optimised. This, over the lifetime of an aeroplane, could lead to appropriate noise levels in the cabin whilst achieving potential reductions in fuel consumption, emissions and costs.
Supervisor: Mcalpine, Alan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available