Auralization of Flyover Noise from Open-Rotor Engines Using Model-Scale Test Data

Abstract

A series of model-scale tests were recently completed using the open-rotor propulsion rig at the NASA John H. Glenn Research Center at Lewis Field in an effort to characterize the aeroacoustic performance of several open-rotorpropulsor designs. These included the historical-baseline and second-generation blade sets. Subsequently, the second generation design was assessed to have significant cumulative margins relative to the International Civil Aviation Organization Chapter 4 noise regulations, whilst the historical blade set had a negative margin. However, integrated metrics, like effective perceived-noise level, are not intuitive to the layperson, and likely do not convey the noise benefits over earlier designs, for example, the acoustically unique unducted-fan demonstrator of the 1980s. This paper develops the means of auralizing flyover-noise projections of full scale open-rotor engines using model-scale data in a manner that more readily communicates the noise benefit, and that is consistent with previously published aircraftsystem-noise assessments. The effects of thrust level, installation type, and rotor-inflow angle on the generated flyover noise are investigated for the historical-baseline blade set. Finally, the benefits of the modern open-rotor blade design are made apparent through comparison of flyover noise from the second-generation and historical-baseline blade sets.