Design methodologies for aircraft noise estimation with parametric analysis

A major challenge in the transport sector is to make economic growth compatible
with environmental constraints, while remaining competitive and innovative. The
loose integration of engine models into iterative design workflows has prevented aircraft
manufacturers from implementing efficient, cost-effective solutions. The search
for a new paradigm has led European programmes such as Clean Sky 2 to coordinate
and finance research activities aimed at delivering a more sustainable aviation with
reduced gas emissions and noise levels. Among these, the ADORNO project has
originated from the partnership of the University of Naples with MTU Aero Engines
and Lead Tech. Its objectives include the development of a computer method
for the prediction of aircraft noise, allowing to consider acoustic emissions from
the early stages of design processes. In order to accelerate the attainment of this
goal, the candidate has completed an internship activity at the headquarters of MTU.

The new software had to comply with several constraints concerning compatibility
with the development environments in use at MTU. The new code had to be written
in C++, following the paradigms of object-oriented programming. It had to rely on
methods capable of predicting the noise generated by moving turbofan aircraft, with
reference to microphones placed at arbitrary positions, including both aerodynamic
and propulsive sources as well as the effects of sound propagation in the atmosphere.

Based on a pre-existing MATLAB code developed at UNINA, the new program
has been redesigned by the candidate and named ATTILA++. The employed
semi-empirical methods, provided by some ESDU Items, allow to calculate the
aerodynamic noise starting from a few geometric data. The engine noise is calculated
by external programs and given to the software as additional input. All contributions
are adjusted for atmospheric attenuation, ground reflection and lateral attenuation.

The first version of ATTILA++ has been completed in compliance with the technical
requirements. In order to test its potential, a parametric analysis of the airframe
noise has been conducted on a specific regional aircraft, with the main objective of
identifying the geometric parameters with the greatest impact on the total noise
level. Preliminary results have shown that efforts made to reduce aerodynamic noise
are rewarded only in the approach conditions envisaged by the regulatory authority.
It has been found that switching from single- to triple-slotted flaps can lead to an
increase of + 3.2 dB in airframe noise and + 1.7 dB in the total effective perceived
noise level (EPNL). Reducing the flap deflection by 10° has resulted in a reduction
of 0.34 % in the total EPNL. Doubling the main wheels has increased the EPNL
by 0.53 %, while halving their diameter has led to − 0.26 %. Lastly, the acoustic
footprints left by the aircraft during take-off and landing have been reproduced