Application of a High-Order FEM Solver to Aeroengine Exhaust Noise Radiation
Regular paper
Siemens Industry Software NV
Wednesday 3 june, 2015, 08:40 - 09:00
0.3 Copenhagen (49)
Abstract:
The propagation of sound in complex flows is a critical issue for many
industries. Most Computational Aero Acoustics propagation methods currently in
use in industry are based on the full potential theory which cannot properly
describe sound propagation through complex sheared flows. When dealing with
turbomachinery noise radiated from the engine exhaust, a strong refraction
occurs through the jet shear layer. To better represent the physics at hand one
can solve instead the Linearised Euler Equations (LEE). However time-domain LEE
models have shortcomings for industrial applications, such as the presence of
linear instabilities and the stability of impedance models. Most of these issues
can be avoided by resolving the LEE in the frequency domain. However, this can
be very demanding because of the high memory requirements associated with
solving large sparse linear systems. For high frequency, the standard finite
element method (FEM) is known to suffer from large dispersion errors. Its
straightforward application to the LEE, which involve up to five unknowns in 3D,
would be computationally costly. To address these issues, an alternative
approach based on high-order FEM is presented in this paper. A discretised
axisymmetric form of the LEE is described in conjunction with Perfectly Matched
Layers. In addition, a numerical stabilisation scheme of type Galerkin/Least-
Squares is included in the numerical model. The proposed method is validated
against reference analytical solutions for a problem of sound propagation from a
semi-infinite circular duct for different mean flow configurations. The sound
propagation and radiation are accurately described, as well as the interaction
between the acoustic waves and the hydrodynamic field resulting in the vorticity
shedding from the duct lip.