Boundary Layer Ingestion Ducted Fan: Aeroacoustic and Psychoacoustic Insights

An in-depth experimental study was conducted to investigate the noise characteristics of a ducted fan ingesting an adverse pressure gradient turbulent boundary layer, typical of those encountered in novel airframe-integrated propulsion systems. To gain insights into the fundamental mechanisms underlying far-field propagation and perception, an integrated approach combining aeroacoustics and psychoacoustics assessment was employed across various thrust regimes. A detailed comparison is made between the isolated and installed configuration of ducted fan to understand the relationship between noise and annoyance associated with Boundary Layer Ingesting (BLI) ducted fan. The study demonstrates how interactions between the incoming turbulent boundary layer and the ducted fan alter the acoustic field, thereby influencing the far-field noise propagation and its perception. Aeroacoustic assessments indicate that the installed configurations, especially at higher thrust levels, lead to increased Sound Pressure Levels (SPLs) due to pronounced interactions with turbulent boundary layers. The psychoacoustic evaluation reveals significant variations in noise perception as a consequence of the BLI installation of a ducted fan, identifying the Loudness as a dominant factor in Psychoacoustic Annoyance (PA), particularly in the upstream region. Roughness and Sharpness play a complementary role in PA at the position of the duct lip, and in the upstream and downstream regions, respectively.