Aeropropulsive Design Optimization Studies of a Blended Wing Body Aircraft

Abstract

With the increasing demand for flights, the environmental impact of aviation is on the rise. To tackle this challenge, it is necessary to look into the design of unconventional aircraft configurations and engine design improvements to improve overall fuel efficiency. The Blended Wing Body (BWB) aircraft is one of the most promising unconventional configurations for future airliners. Several studies have looked at the design optimization of the BWB and its engine-integration effects. However, most of these studies were limited by either a lack of coupling between the aerodynamic and propulsion models or restricted design freedom for nacelle design and engine-airframe integration. Thus, there is a need to explore the benefits of aeropropulsive trade-offs using non-axisymmetric nacelle designs and refining its relative placement above the wing.

The work performed in this thesis focuses on realizing these aeropropulsive trade-offs by optimizing the engine and the BWB wing simultaneously using selectively non-axisymmetric engine design variables, including design variables for wing shape and engine placement. To achieve this objective, a free-form deformation (FFD) based parameterization scheme is developed for non-axisymmetric engine parameterization along with design variables for modifying wing shape and relative engine placement. ADflow CFD solver is used for the aerodynamic discipline, and the PyCycle thermodynamic cycle library is used for the propulsion discipline. Coupled aeropropulsive optimizations are performed by extending the MACH-Aero framework using coupled derivatives in an Individual Discipline Feasible (IDF) architecture for gradient-based optimization using the SNOPT optimization algorithm.

A set of studies are performed to establish the robustness and effectiveness of the proposed FFD-based parameterization for engine optimization in isolation. Later, the engine is mounted onto the BWB in an over-the-wing configuration, and the effect of non-axisymmetric engine design is explored in conjunction with engine placement and wing shape modifications. Optimizing the engine location with axisymmetric nacelle and wing shape design variables reduces the wing drag by 11.5% and engine fuel consumption by 2.3% compared to the baseline engine location. Using non-axisymmetric nacelle design variables further drops the fuel consumption by 1.1%. A comparison of this optimized engine-airframe design with an optimized engine in isolation shows that placing the engine in an over-the-wing configuration with the BWB reduces the thrust-specific fuel consumption by 4.4%. Non-axisymmetric nacelle design also improves the quality of engine inflow by eliminating local super velocities at the inlet lip. This study shows the benefits of an OWN configuration for the BWB and quantifies the performance gains from optimizing the engine location with non-axisymmetric nacelles.