Evaluation of High-Fidelity Multidisciplinary Sensitivity-Analysis Framework for Multipoint Rotorcraft Optimization

Abstract

A multidisciplinary gradient-based sensitivity-analysis methodology is evaluated for optimization of rotorcraft configurations. The tightly coupled discipline models include physics-based fluid dynamics and rotorcraft comprehensive analysis. A discretely consistent adjoint method accounts for sensitivities of the unsteady flow and unstructured, dynamic, overset grids; whereas sensitivities of structural responses to aerodynamic loads are computed using a complex-variable method. The methodology is applied to optimize the shape of UH-60A Blackhawk helicopter blades for hover and forward-flight conditions. The objective of the multipoint design is to simultaneously increase the rotorcraft figure of merit in hover flight and reduce the rotor power in forward flight. Trimmed loose-coupling solutions for the baseline configuration are used to initiate the tight-coupling multidisciplinary analysis. The target thrust, rolling moment, and pitching moment are enforced as optimization constraints. The optimized configuration improves the optimization metrics at both design points. The improved performance and all constraints are maintained over many revolutions beyond the optimization interval, satisfying the required flight conditions. The computational cost of the optimization cycle is assessed in a high-performance computing environment and found affordable for design of rotorcraft in general level-flight conditions.