Prediction of Inlet Tone Noise From Two-Stage Fans

Prediction of noise from two-stage fans that would likely power some of the proposed civil supersonic passenger aircraft concepts under development is an important element of the design of turbofan engines that could meet both the landing and takeoff noise regulations while providing efficient performance at the supersonic cruise. Existing noise databases, and most of the available empirical fan noise prediction models, were developed with a focus on the subsonic engine fan noise and as such have large uncertainties in predicting the noise from two-stage fans designed for supersonic applications. The problem is further complicated because such fans operate in the presence of inflow distortions caused by the complex inlet systems with which they are coupled. To address these complexities, the NASA Commercial Supersonic Technology Project has focused on the use of physics-based noise prediction tools for supersonic-relevant fan-inlet systems. This paper and a companion one, summarize this effort, which is currently focused on the fan inlet tone noise though it is also applicable to the fan exhaust tone noise. The methodology adopted for this work along with some of the recent results will be presented in this paper.