Aeroacoustic Emissions from Quadcopter Unmanned Aircraft Systems as Quadrupoles

Comparison in accuracy for a series expansion and a quadrupole representation of an acoustic source is completed utilizing static acoustic measurements on three candidate Unmanned Aircraft Systems (UASs). Complex representations of acoustic emissions do not always provide the most physically accurate or intuitive description. Creation of a multipole expansion of acoustic emissions provides insights to design and configuration of future UASs. Acoustic quadrupole source representations are constructed from first principles. The quadrupole source descriptions are compared with a spherical harmonic series expansion to determine the adequacy of each. The unknown coefficients are determined from measurements accomplished at the Owens-Corning Acoustic Test Facility. The output of the models is compared to six additional measurement sites excluded from the source construction. The quadrupole and series expansion both represent the acoustic emission patterns adequately. The quadrupole's physical based representation shows that the noise emitted from the aircraft is less defined by the individual propeller-engine combination and more based on a monopole source representation.