Z08: low-speed aero-acoustic experimental characterization of open rotor installation on aircraft

Airbus carried out an extensive test campaign named Z08, in cooperation with Snecma and Rolls-Royce, between spring 2012 and early 2013 to characterize the low-speed aeroacoustics behaviour of an open rotor for several levels of aircraft installation. The test campaign was done in the DNW-LLF open jet wind tunnel. The test setups included an isolated engine configuration, a configuration with the engine mounted behind a supporting pylon and a representative aircraft with two rear-mounted engines in a Pusher configuration. The pylons were equipped with a blowing system designed to reduce the blade passing frequency tones. In addition to AI-PX7 generic blades designed by Airbus, Snecma and Rolls-Royce provided advanced blade designs. Besides the usual DNW out-of-flow microphones, an in-flow acoustic instrumentation was used to enlarge the polar and azimuthal angular range measured, to have a high spatial resolution of the measured noisefield and to avoid the noise propagation issues through the wind tunnel shear layer. This paper presents a few test results with the AI-PX7 blades regarding open rotor installation effects for the Pusher aircraft. As an example, the test analysis highlights that the open rotor aircraft installation results in additional noise sources on front rotor blade passing frequencies compared to the isolated with pylon configuration. It also shows that the acoustic benefit of pylon blowing is confirmed on the aircraft configuration. Open rotor acoustic installation effects mitigation is indeed not limited to pylon blowing optimisation. The Z08 test campaign confirmed the need to carefully handle open rotor propulsion system installation with the aim of minimising inflow distortions into the propeller disks and consequently decrease its acoustic impact.