UC Irvine

Advances in distributed electric propulsion (DEP) have enabled novel propulsor architectures and operating capabilities for short takeoff and landing (STOL) and vertical takeoff and landing (VTOL) aircraft. The noise produced by these architectures is strongly dependent on propulsor design and operating state, while their expanded operating capabilities enable unconventional flight profiles within relatively small ground footprints. Together, these characteristics cause community noise to depend on both propulsor source noise and the aircraft operating states encountered throughout the flight profile. The potential operation of Advanced Air Mobility (AAM) aircraft near populated areas further motivates an integrated approach to propulsor design, aircraft performance, and source- and community-noise assessment. The objective of this thesis is to develop a methodology for designing and evaluating propulsors and DEP architectures and to examine how propulsor geometry, arrangement, operation, and flight path affect aircraft performance, source noise, and community noise. Propulsors are designed from limited top-level vehicle geometry and performance requirements using blade element momentum theory. Propulsor performance is coupled with physics-based vehicle models to generate representative flight profiles for DEP STOL and VTOL aircraft. Tonal and broadband source noise are modeled using Ffowcs Williams--Hawkings and Brooks, Pope, and Marcolini methods, respectively. The resulting source-noise hemispheres are propagated along the flight profiles to evaluate the coupled effects of propulsor design and aircraft operation on community noise. The methodology is further integrated with motor and nacelle sizing and aircraft performance models to evaluate DEP arrangements for a representative regional turboprop aircraft. The results demonstrate strong coupling between propulsor design, performance, and noise. Propulsor geometry and operation significantly affect source noise and required power, with lower tip speeds generally reducing noise at the expense of increased torque or power for some designs. Changes in DEP arrangement further alter lift augmentation, required thrust, power, and noise, demonstrating that propulsor count cannot be considered independently of propulsor design and operation. Application to representative STOL and VTOL aircraft demonstrates that community noise depends on both source-noise magnitude and flight trajectory, as changes in propulsor operation also affect aircraft altitude and the duration of high-noise flight segments. Consequently, reductions in source noise do not necessarily produce equivalent reductions in community noise. At the aircraft-system level, integration of motor and nacelle sizing, aircraft performance, and operating constraints shifts the preferred DEP design space, demonstrating that propulsor performance alone is insufficient for aircraft-level design selection. For the regional turboprop application, low-noise DEP arrangements overlap with designs having low fuel consumption, while lower propulsor tip speeds enable higher-speed operation than conventional turboprop propulsors. Engine core noise also becomes increasingly important as DEP propulsor noise is reduced at lower tip speeds. Overall, the methodology provides a framework for evaluating the coupled effects of propulsor design and arrangement, aircraft performance and operation, source noise, and community noise during preliminary aircraft design.