Acoustic characterisation of double-orifice configurations by means of a LES-SI approach

Regular paper

Carlo Sovardi

TU München, LS für Thermodynamik

Wednesday 3 june, 2015, 10:20 - 10:40

0.3 Copenhagen (49)

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.

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