Acoustic Test Method for Turbofan Engine Exhaust Systems at Cruise Conditions

The exhaust flow from a turbofan engine operating at typical cruise conditions generates noise as turbulent flow interacts with the basic shock cell pattern. This can be a significant source of noise within the aircraft cabin. The proposed innovation is a new method for testing the acoustics of model scale turbofan engine exhaust systems at cruise conditions in a transonic wind tunnel. This would complement the aerodynamic tests now conducted in the wind tunnel. Currently, acoustic data at cruise conditions is only obtained from costly flight tests. Wind tunnel tests are desirable to simulate the proper flight conditions, but acoustic measurements are difficult in this environment. Microphone arrays and specialized array processing techniques are required to separate model noise from tunnel induced noise and reverberation. The new method involves three specific areas of innovation: a) phased-array noise measurement methods, b) evaluating potential modifications to an existing wind tunnel, and c) evaluating means for reducing model air supply noise. Preliminary measurements demonstrate that each of these problems is solvable. The proposed research will then lead to a successful commercial ?service? to airframe manufacturers interested in increasing passenger comfort through better understanding of the noise sources that influence the passenger cabin environment.