Structural optimization of flight vehicles with non-linear aerodynamic loads

Abstract

Introduction The paper presents a methodology of performing structural optimization with static aeroelastic considerations, where the aerodynamic loads are provided by non-linear computational fluid dynamics (CFD) schemes. Two main subjects that are studied are the computation of airloads on a maneuvering flexible aircraft within CFD analysis, and their integration with a structural optimization code. The analysis and optimization processes are based on a CFD code originally developed for solving the Euler or Navier-Stokes equations for a fixed-shape configuration. The main difficulty in interfacing CFD analyses with structural optimization arises from the fact that the CFD analysis is computationally intensive, and that repeated analyses are required during the structural optimization. This difficulty is overcome by performing several aeroelastic trim corrections and optimization runs during the process of CFD flow field convergence, such that the aerodynamic loads and the structural design are converged simultaneously. A modal structural model is used for elastic shape updates, and a trim corrections algorithm is used for varying the incidences and control surface deflections for obtaining the user-defined maneuvers. The CFD maneuver loads can define some of the loading cases in a multidisciplinary structural optimization scheme. The method is demonstrated with a realistic wing-fuselage-elevator transport aircraft model performing symmetric and antisymmetric maneuvers at Mach 0.85. The number of iterations required for convergence of the combined maneuver-optimization analysis is typically almost the same as that of the regular CFD analysis for a fixed shape.