Acoustic characterisation of double-orifice configurations by means of a LES-SI approach
Regular paper
TU München, LS für Thermodynamik
Wednesday 3 june, 2015, 10:20 - 10:40
0.3 Copenhagen (49)
Abstract:
Numerical prediction of turbulent noise as well as acoustic propagation in
ducted flows are challenging
problems in modern computational aeroacoustics.
Present numerical studies based on Linearized Euler Equations or Large Eddy
Simulations are focused either
on the acoustic scattering or on the noise determination. A systematic,
concurrent study of both effects is
still missing.
Multiport and Plane Wave Decomposition methods can be used to obtain a low-
order description of these
phenomena. Thereby, the acoustic propagation in a duct system is modelled in
terms of reflection and
transmission coefficients through the so-called scattering matrix.
Additionally, noise source terms are
introduced in order to characterise the noise generation in the domain.
Within this study we aim to assess concurrently both scattering matrix and
noise term by means of the so-
called LES-SI method. At first, an Large Eddy Simulation of compressible flow
is carried out, with broad-
band acoustical excitation at the boundaries. Subsequently acoustic data
series extracted from LES are
post-processed by means of System Identification techniques to assess the
acoustic propagation and the
turbulent noise sources in the ducted flow under analysis.
The work is focused on duct singularities such as orifices, diaphragms or
mufflers, where noise generated
by turbulence is particularly important. Non linear phenomena may result from
acoustic and flow
interactions. A systematic description will be carried out, in the linear
regime, by mean of the Box-Jenkins
model, which is an extension of correlation analysis that affords a dynamic
model of the noise sources. In
case of nonlinearities, a more general nonlinear model based on Neural
Networks is employed. The results
are validated against experiment.
This analysis is carried out in the framework of the European Project 289352,
FLOWAIRS.