Junis Abdel Hay, SciComp

Title:
Modelling Real Acoustic Absorbers for Computational Aeroacoustics

Abstract:

Acoustic liners are widely used as acoustic absorbers in the inlet and bypass duct of aero-engines. Commonly used acoustic liners are Helmholtz resonator arrays and consist of a rectangular or honeycomb cell structure which is covered by a perforated facesheet. As far as aero-engines are concerned drainage slots are cut into the resonator walls. Therefore, these resonators are exchanging fluid and are considered to behave non-locally reacting. The behaviour of locally reacting liners can be described by the acoustic impedance. Currently, there is no method to directly measure the impedance under flow conditions but it can be calculated indirectly by an impedance eduction. Therefore, a liner model is used to include lined surfaces in Computational AeroAcoustic (CAA) simulations. The model’s parameters must be optimized to reproduce the measured liner characteristics. The optimized parameters can be used to predict the liner behaviour for complex geometries and with flow. For some novel liner concepts or non-locally reacting liners, the behaviour is too complex to be accurately reproduced by models based on simple physical assumptions. This issue is investigated based on impedance eductions for locally and non-locally reacting liners using different liner models and optimization methods. The effects of the non-locally reacting behavior will be discussed and the applicability of these different methods is reviewed. An analytical model for two coupled non-locally reacting Helmholtz resonators is presented and the structure of the model parameters will be discussed. The effects generated by the propagation of sound through the cavities are identified. The model is validated based on CAA simulations of this configuration with normal sound incidence. Furthermore, the results are compared to the experimental data and the model is extended empirically.