B1.3- Physics of broadband noise of sound sources from installed propulsors

For aircraft with tightly integrated propulsors, not only the propulsors alone are sources of tonal noise, but their integration with the aircraft generates excess noise. For instance, even the installation of a propeller in front of a wing, usually considered to result in moderate excess noise, may increase the dominant sound pressure level of the propeller harmonics by roughly 10dB, along with a change of directivity to more omnidirectional radiation. For propulsion systems designed for low tonal noise, broadband sound generation may become dominant, again particularly in the aircraft-integrated situation. To be considered in the assessment of different a/c design variants (currently not possible), the physical mechanisms behind the generation of broadband sources of installation noise need to be understood, and cast into a source model. This project will develop this knowledge and source model. Three key broadband source mechanisms are foreseen to be dominant and will be addressed:

• blade self noise (trailing edge noise);
• blade leading edge noise from inflow turbulence;
• interaction noise at a/c components due to the rotor’s downstream wake turbulence.

The proposed project takes the challenge of understanding complex flow physics, relating this to the near- and far-field acoustic fields, and use this understanding and performed analysis to define a source model useful for psychoacoustic assessment of cabin noise, as well as flight route optimization studies for minimal noise hindrance. The key research questions are:

• Which of the three source mechanisms dominate broadband noise as a function of operation/integration, and in which frequency range? (is there one, which may be neglected?)
• How does the composition of tone and broadband noise look like for the SE²A propeller aircraft concept in terms of community noise and cabin noise?
• Can one generalize the interaction noise mechanisms for a representative propeller-wing configuration into a source model useful for aircraft trajectory or design optimizations, and which are the driving parameters that define the outputs and accuracy of such method?