Coupled Aeropropulsive Design Optimization of an Over-wing Nacelle Configuration

Abstract

The over-wing nacelle (OWN) configuration has the potential to improve on the conventional under-wing nacelle (UWN) configuration by enabling higher bypass ratios and increasing noise shielding. To explore this potential, we perform coupled aeropropulsive design optimization to study the coupled analysis and the design tradeoffs between aerodynamics and propulsion. We find that the variations in wing shape are not significant when the OWN configuration is optimized for different fan pressure ratios. Optimizing the OWN configuration using the proposed approach results in 3% less shaft power than optimizing the wing and propulsor separately. The OWN has marginally superior performance over the UWN for the same lower fan pressure ratio. However, this low fan pressure ratio may be unattainable for the UWN configuration because of ground clearance constraints, whereas the OWN configuration is not subject to such constraints. We study the optimal OWN placement and show that placing it aft of the trailing edge and away from the wing root results in lower required shaft power. In this study, we perform single-point optimizations to understand the fundamentals of the OWN configuration in terms of aerodynamics and propulsion. However, multiple operating conditions, structural integrity, and inclusion of the pylon geometry should be considered to assess the net benefit of the OWN configuration. Nevertheless, these advancements in aeropropulsive optimization are critical to OWN configuration design and more sustainable aircraft.