A gradient-based aero-stealth optimization design method for flying wing aircraft

Abstract

Flying wing layout has both favorable aerodynamic performance and outstanding radar scattering characteristics, which is regarded as an ideal stealth aircraft layout. In this paper, a gradient-based aerodynamic and stealth optimization design method is established by coupling the Free-Form Deformation approach (FFD), Radial Basis Function algorithm (RBF), Computational Fluid Dynamics (CFD), Physical Optics (PO) and the Sequential Quadratic Programming algorithm (SQP). The gradient of the aerodynamic characteristic parameters could be obtained by solving the discrete adjoint equations. With PO code differentiated by the automatic differentiation tool, the Radar Cross Section (RCS) and its gradient would be collected. Based on the aero-stealth optimization design method, three kinds of optimization strategies are applied to design a certain flying wing layout aircraft: 1) The drag coefficient is chosen as the objective function while the RCS is set as a constraint condition; 2) The RCS is selected as the objective function while the drag coefficient is set as a constraint condition; 3) The objective function is composed of the drag coefficient and the RCS through the Weighted Sum method. The optimization results show that when choosing the first two strategies, the optimization algorithm would push single discipline performance to the edge. Alternatively, it would obtain several trade-off configurations when selecting the last strategy. The results demonstrate that the gradient-based aero-stealth optimization design method can deal with the multidisciplinary optimization problems which require a large number of design variables. Without a large number of function evaluations, this method could rapidly and efficiently obtain the shape that meets the requirements of aerodynamic and stealth performances.