Multidisciplinary optimization of aircraft design and takeoff operations for low noise

Abstract

Aircraft planform design, takeoff operations, and airfoil design are examined as a complete system in order to quantify tradeoffs that can result in a quiet aircraft. An aircraft design model was developed to generate blended-wing-body-type designs using simple-physics models and empirical scaling from a reference design. This model generates a scaled airframe and engine, an estimate of aircraft weights and center of gravity, a takeoff trajectory, outer wing airfoil profiles, and takeoff noise predictions. Integrating the model with a single-level optimization framework, it was found that optimization for minimum noise can result in a significant noise reduction on takeoff, primarily due to changes in aircraft design and operations. There exists a design-operations coupling between the departure flight path angle and the engine size which must be exploited. Low-noise designs resulting from the single-level optimization require more fuel to complete the design mission. Modifications to the airfoil profiles do not significantly contribute to further reductions in takeoff noise, but do mitigate the fuel burn increase without adversely affecting noise levels.

(cont.) A distributed optimization framework was constructed from a problem decomposition into three subspaces: aircraft planform and engine design, aircraft operations, and wing design. In this framework, a system level optimizer is responsible for minimizing the system noise while subspace optimizers control the disciplinary models individually. This setup allowed for the exploration of different areas of the design space. As a result, the distributed optimization converged to a fundamentally different design solution with the same minimum noise value as in the single-level optimization, but with a much lower fuel burn. The key contributions of this thesis are the development and quantitative analysis of a weight and center of gravity model for an unconventional aircraft configuration, a distributed optimization framework, and a low noise aircraft design with competitive fuel burn.