关键词: FFD技术, 非均匀有理B样条, 粒子群优化算法, 计算流体力学, 大型运输机, 上翘后体, 气动优化设计

Abstract:

A free-form deformation parameterization (FFD) method is established based on non-uniform rational B-spline (NURBS) basis function. Furthermore, by coupling the transfinite interpolation (TFI) grid deformation technology and computational fluid dynamics (CFD) method with improved particle swarm optimization (PSO) arithmetic,a general aerodynamic optimization design system is constructed. Then, the aerodynamic optimization design system is applied to designing a large upswept afterbody of transport aircraft C17 on the restrictions of nondecreasing maximum structure height, width and upswept angle. The optimized afterbody decreases the total drag by 2.6% and pressure drag by 19.8% respectively. A comparison analysis of the aerodynamic shape and flow pattern reveals that the key factors for the optimized afterbody to decrease the pressure drag greatly are the increased near-roundness of the afterbody cross-section and decreased near-roundness change ratio along the fuselage axis. The two factors enable the adverse pressure gradient along the circumferential direction to become smaller, which can suspend aferbody separation and weaken afterbody vortex strength. The aerodynamic optimization design system constructed in this paper has good practicability and engineering application prospect.

Key words: FFD technique, non-uniform rational B-spline, particle swarm optimization, computational fluid dynamics, large transport aircraft, upswept aferbody, aerodynamic optimization design