Quantification of the Acoustic Emissions of an Electric Ducted Fan Unit

Multiple aircraft manufacturers are developing novel electric aircraft concepts to explore the capabilities of modern electromobility. Their respective electric propulsion systems obtain different turbomachinery properties and ex-
hibit different acoustical behavior than conventional combustion turbines. In collaboration with VOLARE GmbH, acoustic measurements were performed on subsonic electric ducted fans (EDF). The work examined the total sound
power emissions and microphone array measurements to understand the dominant acoustic emissions and their respective prevailing source mechanisms. Measurements at discrete operating points and transient measurements
across the total operating range were conducted to provide complete information on the EDF’s acoustic behavior.
The rotor-self noise and the rotor-stator interaction were identified as primary tonal sound sources, along with the highest broadband noise sources also being located on the rotor.
Additionally, far-field measurements of the unit’s electric powertrain without load were conducted, which showed significant noise emissions from the periodic electromagnetic forces. An unexpected dependence on the
rotational speed was detected in the powertrain’s noise spectrum, contributing to the EDF’s perceived acoustics.
After processing the insights gained from the measuring campaign, a secondary noise reduction measure was designed