Acoustic Design, Modeling, and Initial Flight Test Validation for Ultra-Low Noise Distributed Electric Propulsion Aircraft

During the Phase I effort, an analysis framework was developed to assess the noise of distributed-propulsion blown flap STOL vehicles which utilizes a noise-component based modeling approach to estimate the relevant noise sources based on flight performance requirements. In this framework, noise modeling of vehicles with multiple propellers or rotors uses discrete tonal and broadband noise modeling methods from ANOPP2's Blade Element Acoustic Tool (ABEAT). Multiple rotor interactions noise can be performed analytically in ANOPP using superposition to combine the tone signatures from individual propeller/rotor noise time histories. The propeller wake will also interact with the wing trailing edge and the flaps. This effect has been shown in previous noise measurements of blown lift-flap interaction noise to scale with approximately the 6th power of the jet velocity. Additional propulsor-airframe interaction effects are estimated through modified usage of the airframe noise modules. Additional noise at the flap and wing trailing edge is assumed to be impacted due to the increased local flow velocity from the propeller wake compared to aircraft without distributed blown lift. To include this effect, the propeller wake-flap and propeller wake-trailing edge interaction noise is approximated using ANOPP’s built-in Guo flap side edge noise and Fink trailing edge noise models, incorporating the estimated propeller wake velocity in different operations. This effect will be studied in further detail during the Phase II activity. To demonstrate the current functionality of the noise analysis method, example modeled sound exposure level (SEL) noise contours obtained from the developed noise modeling methods for observers at the ground level for the propeller, airframe, and total noise components during a representative continuous descent, blown-flap approach operation. The propeller noise dominates, but the airframe noise, mostly from the propeller wake-flap interaction noise, extends the 70 dB level of the total noise. Similar analysis was performed for a representative departure procedure, which showed that airframe noise was small compared to propeller noise. This demonstrates the method's capability to assess community noise impacts of the STOL vehicle. Similar analysis will be performed for additional flight procedures. The resultant Phase II methods will be used to design components with lower source noise levels (such as propellers) as well as flight operations for both lower source noise levels and community noise exposure levels.