EFFECT OF UNIFORM FLOW ON LINER ATTENUATION PREDICTION IN AERO-ENGINE

The prediction of the noise generated by aero-engine components in flight condition is an important tool for the aircraft design process. In some of these conditions, the fan noise generated by the rotor-OGV stage at a given blade passing frequency can be modeled as acoustic modes, which are used to compute the in-duct acoustic field as well the acoustic far field. In order to reduce fan noise, acoustic liners are used for noise control, and are generally assumed as an acoustic impedance. However, on flow conditions, the acoustic absorbing properties of liners properties and the resulting noise reduction may be affected, which can lead to a reduction in their efficiency. As a consequence, the directivity of the far-field sound is also modified. The main goal of this study is the development and validation of a prediction tool that computes the effect of liner attenuation in the far-field directivity pattern, including uniform mean flows. The study was conducted considering typical engine dimensions and operating conditions. A reference solution was obtained from a finite element method code and used to validate the analytical model, based on the mode-matching technique and an analytic radiation model. Finally, the results suggest the prediction tool provides good agreement with reference solution and that the influence convective effects can modify liner attenuation and far-field directivities.