Acoustics of future aircraft

The project's primary objective will include the modelling of the sound radiation and scatteringon the fuselage of an Ultra High By-Pass Ratio turbofan engine using analytical methods. Previ-
ous work that has been carried out assumed an axisymmetric flow in the intake, and considered
the sound radiating out of it as a single spinning mode. In this project, the intake problem will
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be solved in three dimensions meaning that the velocity will vary circumferentially around the
intake duct, thus giving a more realistic description of the inlet flow. Furthermore, this project
will include multiple modes exiting the fan adding to the complexity of the problem but also
rendering it more realistic, since the radiated field will be fully three-dimensional.
After determining the radiation the next objective will be to model the scattering on the fuselage
which is the most important installation effect, using analytical methods. The presence of the
fuselage affects the resulting sound field on the surface of the fuselage but also in the far field.
Previous work focused only on the fuselage pressure levels whereas this project will also focus on
the calculation of the far-field pressure. This will greatly improve on our knowledge of the impact
the aircraft noise has on the ground. Moreover, this project will also focus on the calculation of
the pressure field for multiple frequencies trying to discover any trends between varying frequency
bands and the resulting noise level. These objectives will be incorporated in a well-documented
and usable code for industry. Thus, the code will enable future researchers working on instal-
lation effects within Rolls-Royce to conduct parametric studies by varying the inputs of the code.
The project also has some secondary objectives. One of these will be to conduct a parametric
study. The pressure field will be calculated for varying airframe geometries and positions of the
turbofan engine. Thus, the optimal positioning of the Ultra Fan can be estimated. Another
objective will be to introduce scattering on a flat plate in order to model the scattering of the
fan noise on the wing or tail of the aircraft. Finally, another objective will be to analytically
model the scattering on a fuselage which has a varying boundary layer thickness. Previous work
included the effect of the boundary layer along the fuselage but it was assumed to have a con-
stant thickness which is not realistic during flight. The installation effect of the boundary layer
is of great importance as it introduces a refraction effect that tends to substantially decrease
the fuselage pressure levels on certain areas upstream of the engine. As a result, this determines
where most of the lagging must be installed avoiding excess lagging where it is not needed which
results in less weight. Therefore, it would be of great significance to gain insight into the problem
with a varying boundary layer thickness.
As it has already been mentioned, in this project the problems in question will be solved using
analytical and theoretical methods. Analytical methods pose a great advantage over the com-
putational ones because of the reduced computation time they require to produce results. In
order to progress in this area, a thorough knowledge on Fourier methods is required as they are
used to reduce the complicated differential equations into algebraic ones. Furthermore, a good
background on duct acoustics is beneficial as the radiating sound is modelled using spinning
modes exiting the intake duct. Also, since the project will be focused on the far field as well
as the near field, assymptotic methods must be reviewed and investigated. Apart from that, a
good review of numerical integration methods will be beneficial as they will be used either on
performing inverse Fourier transform or on the Frobenius method which integrates the solution
inside the boundary layer.