Multidisciplinary Design Optimization of an Aircraft Considering Path-Dependent Performance

Abstract

Aircraft are multidisciplinary systems that are challenging to design due to interactions between the subsystems. The relevant disciplines, such as aerodynamic, thermal, and propulsion systems, must be considered simultaneously using a path-dependent formulation to accurately assess aircraft performance. The overarching contribution of this work is the construction and exploration of a coupled aero-thermal-propulsive-mission multidisciplinary model to optimize supersonic aircraft considering their path-dependent performance.

First, the mission, thermal, and propulsion disciplines are examined in detail. The aerostructural design and mission of a morphing-wing aircraft is optimized before the optimal flight profile for a supersonic strike mission is investigated. Then a fuel thermal management system, commonly used to dissipate excess thermal energy from supersonic aircraft, is constructed and presented. Engine design is then investigated through two main applications: multipoint optimization of a variable-cycle engine and coupled thermal-engine optimization considering a bypass duct heat exchanger.

This culminates into a fully-coupled path-dependent mission optimization problem considering the aerodynamic, propulsion, and thermal systems. This large-scale optimization problem captures non-intuitive design trades that single disciplinary models and path-independent methods cannot resolve. Although the focal application is a supersonic aircraft, the methods presented here are applicable to any air or space vehicle and other path-dependent problems.

This level of highly-coupled design optimization considering these disciplines has not been performed before. The framework, modeling, and results from this dissertation will be useful for designers of commercial and military aircraft. Specifically, optimizing the design and trajectory of commercial aircraft to minimize fuel usage leads to a more sustainable and more connected world as the rate of air travel continues to increase. The methods presented are flexible and powerful enough to design supersonic military aircraft systems, as demonstrated using an application aircraft. This dissertation has been shaped through direct collaborations with NASA, the Air Force Research Lab (AFRL), and other academic institutions, which shows the broad appeal and applicability of this work to a multitude of design problems.