Robust Acoustic Objective Functions and Sensitivities in Adjoint-Based Design Optimizations

The multidisciplinary design of aircraft typically includes considerations of performance, weight, fuel burn, and noise, among other factors. Objective functions and constraints reflect these considerations to weigh the tradeoff between different designs. Higher-fidelity optimization exercises have used an adjoint approach to reach an optimal set of aerodynamic objective functions, such as increased lift and reduced drag. The adjoint approach significantly reduces the computational time required to find an optimal configuration when there are many design parameters and few objective functions and constraints. Including acoustics in an adjoint-based design optimization requires the sensitivity of acoustic objective functions with respect to design parameters. This paper presents an approach for defining the sensitivity of several acoustic objective functions, including time-integrated metrics, such as effective perceived noise level, and frequency-integrated metrics, such as overall sound-pressure level. A demonstration, validation, and details on the sensitivity analysis implementation in the second-generation Aircraft Noise Prediction Program are also shown.