Coupled aeropropulsive design optimization of a podded electric propulsor

Some novel aircraft concepts use unconventional propulsion technologies to reduce energy usage. Innovative technologies like distributed electric propulsion and boundary layer ingestion introduce new design challenges with airframe-propulsion integration. When designed in isolation, neither the airframe nor the propulsion system achieves maximum efficiency. Thus, a coupled aeropropulsive design optimization strategy is required. The advent of aeropropulsive design optimization solves this problem by simultaneously optimizing the airframe and propulsion system with coupled physics-based models. Despite its advantages, aeropropulsive design optimization has been limited by poor robustness in optimization convergence and a lack of fully coupled models suitable for gradient-based optimization. In this work, we demonstrate two aeropropulsive coupling methods in computational fluid dynamics based models that simulate the coupled effects of the propulsion system and the airframe. The first method uses momentum and energy source terms, the actuator zone model, to model the effect of the propulsion system, while the second uses powered boundary conditions, the boundary condition model. To showcase the effectiveness, we apply each coupled approach to a podded electric fan model based on NASA's STARC-ABL concept. We demonstrate the robustness and efficiency of the approach by performing a design parameter study with 50 aeropropulsive design optimizations. We also perform a multipoint design optimization problem. The optimization maximizes cruise performance subject to a fan-face distortion constraint at rolling take-off conditions. The aeropropulsive coupling strategies we present in this work are crucial for future aeropropulsive design optimizations considering complex propulsion systems and airframe-propulsion integration.