Effect of Rotor Wake Structure on Fan Interaction Tone Noise

The prediction of noise produced by fan wake interaction with the fan exit guide vane is studied. The acoustic response of the fan exit guide vane is computed using LINFLUX, a three-dimensional frequency-domain linearized Euler solver for turbomachinery. The research focuses on tonal noise predictions for the advanced ducted propulsor and the source-diagnostic-test-scaled turbofan rigs. The sensitivity of the two-blade-passage-frequency noise prediction to the inflow specification is investigated. Inflow models are generated based on both experimental and computational fan wake data. The computational data are provided by four different Reynolds-averaged Navier- Stokes computational fluid dynamic solutions. When compared with experimental results, the computations provide comparable mean flow solutions but overpredict the wake deficit. This paper demonstrates how these wake differences translate into differences in the input values used with LINFLUX and then differences in the tonal noise prediction. It is shown that the use of a consistent method of prediction (for example, input based on computational data from one code at each rotor speed) leads to correct trend prediction. While the predictions agree well with each other and capture the trend correctly, they vary from the experimentally measured acoustic sound power levels by up to 14 dB. [PUBLICATION ABSTRACT]