Design-Oriented Computational Fluid Dynamics-Based Unsteady Aerodynamics for Flight-Vehicle Aeroelastic Shape Optimization

Abstract

A design-oriented computational fluid dynamics-based unsteady aerodynamic capability has been developed for the generation of shape sensitivities and approximations of aeroelastic constraints for integration into general flight-vehicle multidisciplinary-design-optimization systems. Complex-variable differentiation was used to convert an Euler unsteady solver with boundary-layer coupling into a design-oriented capability. The resulting shape-sensitivity results have been validated using finite difference method sensitivities on selected lifting surfaces: the AGARD wing, the Cohen wing, and the F-5 wing. Because the complex-variable-differentiation technique is numerically exact, the accuracy of the sensitivity computed by the new capability is step-size independent, whereas that of finite difference methods is highly step-size dependent. The resulting capability is computationally efficient. It covers all flight Mach numbers, including the transonic regime. It is accurate and robust, and interfaces seamlessly with the NASTRAN finite element code, widely used for aircraft design, and with other commercial aeroelastic solvers, such as ZAERO. The present paper focuses on lifting-surface computational fluid dynamics-based unsteady aerodynamics and flutter simulation, and it offers, in addition to the sensitivity-analysis technology described, new insights, not available earlier, regarding the functional dependence of key aeroelastic responses on airplane planform shape, and the accuracy in the cases studied here of Taylor-series-based approximations commonly used in multidisciplinary design optimization.