A parametric study of airframe effects on the noise emission from installed contra-rotating open rotors

Abstract

This work reports on the results of the Clean Sky WENEMOR project which has conducted an extensive experimental investigation of installed contra-rotating open rotors on a scale model of an advanced regional aircraft configuration. The tests were conducted in the Pininfarina Wind Tunnel, Italy and the data used for this analysis were taken from a linear far-field array of microphones. The contra-rotating open rotors were operated in pusher and tractor modes with approach and takeoff settings for revolutions per minute and thrust. Realistic modern blade profiles were supplied and utilized through the Clean Sky Green Regional Aircraft program. A range of airframe geometries was tested which included interchangeable tails, engine pylon elongation, engine pylon rotation, and variable wing to engine distance. Changes in the contra-rotating open rotor noise emission to the far field as a function of flow speed, angle of attack, and airframe geometry were clearly identified. The influence of airframe geometry on contra-rotating open rotor tonal content, directivity, and broadband levels is reported for emission angles from $30°$ to $150°$ . Both significant noise increases and decreases with respect to the baseline airframe configurations were detected in both the tonal and broadband levels as a function of emission angle (ranging from 10 to 25 dB at the blade passing frequency tones). While the changes to the tonal level were generally greater than those of the broadband level, the broadband levels are shown to be significant when considering the influence of airframe geometries on contra-rotating open rotor noise emission.