Prediction of the acoustic influence of an intake on fan flutter: A comparison of numerical methods

Abstract

In certain operating conditions, acoustic propagation and reflection in air intake may have an influence on fan flutter. This paper presents an analytical low fidelity model to evaluate unsteady pressure wave reflected by the inlet. To understand possibilities and limitations of this model, it is compared to acoustic finite element simulations. Although an excellent agreement was found between the model and numerical simulations for a cylindrical intake, quite important gaps are observed for an intake with large lips. The pressure amplitude ratio is globally overestimated and phase lag is obtained with a low precision. The main problematic element seems to be the curved shape of intake lips. Nevertheless, predictions are good enough to locate zones over the compressor map that correspond to a potentially destabilizing phase lag. Possible improvements are the usage of a meridional field as an input to the model and a more accurate modelling of cut-off to cut-on transition.