Turbofan Inlet-Radiated Broadband Acoustic Flight Effects

This paper presents the development of a new model for the prediction of inlet-radiated turbofan broadband noise. The proposed model is developed using data from the Boeing Quiet Technology Demonstrator 2 (QTD2) and the NASA/Boeing Propulsion Airframe Aeroacoustics and Aircraft System Noise (PAA&ASN) flight tests. It is shown that, in contrast to aft-radiated noise, phased array measurements are crucial to isolate inlet-radiated noise and to capture the relevant characteristics of this noise source for modeling. The proposed model is created using data from an acoustically lined inlet, which influences the spectral shape of the model and improves performance over a wider frequency range for in-service aircraft. Directivity characteristics and throttle setting dependence are discussed. Significant improvements over prior methods implemented in the NASA Aircraft Noise Prediction Program are demonstrated, and predicted deltas to measured levels are reduced from +/-10 dB to +/-3 dB at the most relevant frequencies.