Three-Dimensional Aerodynamic/Stealth Optimization Based on Adjoint Sensitivity Analysis for Scattering Problem

Abstract

A radar cross section (RCS) gradient calculation approach based on the discrete adjoint equation of Maxwell integral equation is proposed. The adjoint method can obtain the gradients of all design variables by a single solution of the scattering problem if electric field integral equation is adopted, and by one solution of the scattering problem and one adjoint problem if magnetic field integral equation or combined field integral equation is adopted. Multilevel fast multipole method (MLFMA) is employed in the solution of the scattering and adjoint problem. The accuracy and reliability of the adjoint approach are verified with a double-ogive model. Optimizations considering aerodynamic, stealth, and aerodynamic/stealth performance of a blended-wing–body aircraft with a gradient-based optimizer are conducted. Stealth optimization results indicate that a small leading-edge radius and curvature on the forepart are beneficial to RCS reduction. Aerodynamic performance of aerodynamic optimized model and aero/stealth optimization result are comparable, but stealth performance of aero/stealth optimized result is inferior to stealth optimization. Conflictions between small leading edge and drag reduction are not very prominent based on the current study, whereas curvature is harmful to aerodynamic performance.