战斗机后体流场数值模拟与减阻优化设计

Numerical investigation of jet interactions and optimization design of drag reduction for the afterbody of jet aircraft

采用数值计算方法模拟零迎角跨声速来流下战斗机后体流场,并进行后体外形的减阻优化设计。通过数值求解二维轴对称Navier-Stokes方程、k-ωSST湍流模型和气体组分方程,研究战斗机后体绕流与尾喷流相互耦合的流场特性,对三种欠膨胀喷管压比下的喷流进行数值模拟,同时对比多组分气体喷流和理想气体喷流对后体阻力的影响。采用梯度法对轴对称后体外形进行减阻优化设计,提出一种优化设计加速算法,其基本思路是通过逐步增加设计控制点个数并根据外形曲率合理分布设计控制点的位置,从而改善梯度法的优化效率。计算结果发现,超声速喷流会在后体尾部附近形成复杂的波系结构;与组分气体喷流相比,采用理想气体作为喷流介质时的后体阻力系数略高;在跨声速来流状态下,后体阻力系数值随喷压比的增大而减小。优化结果显示,优化后的的后体阻力系数可以降低13%左右;与一次性均匀分布优化控制点的梯度法优化方法相比,采用提出的优化加速算法可以缩短优化计算时间40%左右,并且可以提高优化设计的精度。

The purpose of this paper is to study transonic flow around the axisymmetric afterbody/nozzle of a jet aircraft at zero incidences,and optimization design for the afterbody.The afterbody/nozzle flow is simulated and analyzed by numerical solutions of 2DReynold-averaged Navier-Stokes equations、k-ωSST turbulence model and species transport equations.The interaction between jet flow and external flow,and influence of afterbody drag between mixture gas and ideal gas,and coupled flowfield of a vehicle at different pressure ratio(NPR)of jet air are investigated.The optimization design of drag reduction for the afterbody shape is carried out by the classical steepest-descent method,and a new algorithm,based on curvature computation of shape,is proposed to improve the optimization efficiency.The number and location of design points are calculated for optimized acceleration by this algorithm.The numerical results show the numerical method can capture the wave structures of jet flow fields,and afterbody drag using ideal gas is higher than that of mixture gas,and the increase of jet pressure ratio brings the reduction of afterbody drag coefficient.Optimization results show that optimized shape brings 13%afterbody drag reduction,compared with original shape. The results also show optimization time reduces of 40%,since the algorithm is combined with steepest-descent method.