A coupled LES/high-order acoustic method for jet noise analysis
Creators: name: Moratilla-Vega, Miguel
Publisher: name: Figshare
Year: 2019
Subjects: subject: Aerospace Engineering
subject: FOS: Mechanical engineering
subject: 99999 Engineering not elsewhere classified
subject: FOS: Other engineering and technologies

description: Aircraft noise is one of the main areas of active research for the aeronautical industry
due to the increasingly stringent regulations on noise emission that aviation authorities
are imposing. Among the different sources that contribute to the total emitted aircraft
noise, jet noise is one of the most important during take-off. Furthermore, as the by-pass
ratio of turbofan engines is increased, the interaction of the jet exhaust with the high-lift
devices and the wing can potentially produce new mechanisms for noise generation. On
the simulation front, the rapid increase of computing power over the last decades is
enabling the use of high-fidelity simulations for the study of jet noise at both industrial
and academic research levels. However, most of the numerical methods used by different
research groups are either too dissipative for propagating the acoustic waves or are limited
to the study of simple configurations. In many cases, surface integral methods have been
the preferred choice with encouraging results for isolated jet configurations. Among these
methods, the Ffowcs Williams-Hawkings (FWH) formulation has been commonly applied
within research communities. However, applying them in complex configurations can
be challenging, which may not provide sufficient information when it comes to studying
noise generation mechanisms.
The work reported in this thesis is devoted to the development of a coupling framework
that is suitable for complex jet noise propagation cases. In this framework, the jet noise
problem is divided into two different steps. First, the acoustic sources are computed
using a robust compressible Large Eddy Simulation (LES) finite volume solver, which
are then transferred to a spectral/hp high-order finite element Acoustic Perturbation
Equations (APE) solver that propagates the sound waves to the far-field.
Two different coupling strategies are investigated. Initially, a simple methodology based
on the exchange of files between the solvers is implemented with only minor modifications
made to the solvers’ source code. However, the poor efficiency of data transfer meant
this method is applicable only to small problems. Thus, a more efficient parallel-interface
coupling technique is developed to overcome this issue. With this technique all the
required data is transferred via a parallel Message Passing Interface (MPI), avoiding the
bottleneck of I/O and file systems. Both coupling techniques are validated with a 2-D
cylinder case demonstrating the superiority of the parallel interface method.
The parallel interface coupling framework is then tested on a low Reynolds number
jet, being validated against experimental and numerical results in the literature, during
which a well-established FWH method is used for references. More promising results
are obtained using the LES/APE method than with the FWH method. The LES/APE
method is then applied to the study of a more realistic isolated jet case and is compared
to the experimental data obtained at NASA. A source analysis is further carried out,
in this case, to reveal the distribution and convection of sources along the jet plume at
different locations. The source distribution is in good agreement with the far-field noise
results.
Finally, the study of a jet-flat plate installed configuration is conducted. This simplified
configuration is representative of a realistic installation scenario and is particularly
useful to the understanding of the installation effects. The coupling framework captures
these additional flow-acoustic effects demonstrating its potential to tackle complex
configurations.