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. ... Read more

The second-generation of supersonic civil transport has to match ambitious targets in terms of noise reduction and efficiency to become economically and environmentally viable. High-fidelity numerical optimization offers a powerful approach to address the complex trade-offs intrinsic to this novel configuration. Past and current research however, despite proving the potential of such design strategy, lacks in deeper insight on final layouts and optimization workflow challenges. Stemming from the necessity to quantify and exploit the potential of modern design tools applied to supersonic aircraft design, this work partially fills the gap in previous research by investigating RANS-based aerodynamic
optimization for both supersonic, transonic and subsonic conditions. The investigation is carried out with the state-of-the-art, gradient-based MDO framework \textit{MACH}, developed at University of Michigan's MDO Lab - which hosted the author for the 14-month research stint. Details of the tool and a brief overview of supersonic aircraft design and modern aerodynamic optimization strategies are reported in the first part of this manuscript.
After circumscribing the research niche, I perform single and multi-point optimization to minimize the drag over an ideal supersonic aircraft flight envelope and assess the influence of physical and numerical parameters on optimization accuracy and reliability. Leading and trailing edge morphing capabilities are introduced to improve the efficiency at transonic and subsonic flight speed by relaxing the trade-offs on clean shape optimization. Benefits in terms of drag reduction are quantified and benchmarked with fixed-edges results. It is observed how the optimized airfoils outperform baseline reference shapes from a minimum of 4\% up to 86\% for different design cases and flight
conditions. The study is then extended to the optimization of a planar, low-aspect-ratio, and low-sweep wing, using the same schematic approach of 2D analysis. I investigate the influence of wing twist alone and twist and shape on cruise performance, obtaining a drag reduction of 6\% and 25\% respectively as the optimizer copes with both viscosity and compressibility effects over the wing. Results for 3D multi-point optimization suggest that the proposed strategy enables a fast and effective design of highly-efficient wings, with drag reduction ranging from a minimum of 24\% up to 74\% for cruise at different speeds and altitudes, including edge deflection. Ultimately, this work provides an extensive and, to the best of author knowledge, unprecedented insight on the optimal design solutions for this specific aircraft configuration and the challenges of the optimization framework. The benefits of RANS-based aerodynamic shape optimization to capture non-intuitive design trade-offs and offer deeper physical insight are ultimately discussed and quantified. Given the promising results in terms of performance improvements and design efficiency, it is hoped that this work will foster the implementation of this method for more comprehensive full-configuration, multidisciplinary supersonic aircraft optimization studies. ... Read more