FLUTTER SENSITIVITY ANALYSIS FOR WING PLANFORM OPTIMIZATION

Kurzfassung

The increased airframe flexibility of the new generation of commercial aircrafts, and the unreliability, for unconventional aircraft configurations, of the classical statistical-based aeroelastic methods, require the introduction of physics-based aeroelastic analysis in the early development stages of the overall aircraft synthesis process. The paper presents a differentiated unsteady aeroelastic analysis module suitable for the large scale MDO problem typical of preliminary aircraft design. Morino's method is implemented and deployed for the frequency domain aerodynamic analysis. This method is able to deal with arbitrary complex 3D body surfaces increasing the geometrical fidelity and the robustness of the analysis procedure. Finite state aerodynamic modeling is adopted to represent the aerodynamic term in the aeroelastic equation allowing the use of simple root locus method for the flutter point definition. The interface with the central data model, CPACS, allows the deployment of the aeroelastic module in collaborative multi-disciplinary design workflows. The total derivative of flutter speed is computed analytically, whereas for some partial derivatives complex step approach resulted more convenient. Since derivatives with respect to wing planform parameters, such us span and sweep angle, are sought, the derivatives of the structural modal shapes cannot be neglected and are analytically computed. For the total derivative of the aerodynamic term in the aeroelastic equation, the GAF matrix, we developed a discrete adjoint method. Finally, the Goland's wing benchmark case is used for flutter analysis validation, and, for this configuration, derivatives with respect to span and sweep angle are computed and compared with finite difference results.