工程约束下基于自由曲面方法的机头气动修形设计

Aerodynamic design of forward fuselage using NURBS with engineering constraints

二次曲线由于其良好的几何特征,在传统的飞机建模过程中得到较多的应用,但是单一的控制参数使其外形变化受到限制,而灵活的外形变化恰是NURBS曲线的主要特点。根据飞机设计过程中总体布局要求及人机工效约束条件,采用NURBS曲线曲面方法,使用控制点位置的相对长度与角度为设计参数,在飞机机头参数化建模过程中融入相关的工程约束,通过CFD计算分析,对设计参数进行优化,得到符合要求的模型;并尝试在风挡区域增加一条横向控制线,调节风挡局部区域的气流流动。结果表明,采用NURBS方法可以得到符合设计要求的机头外形,而且对外形的控制更加灵活;增加风挡区域的横向控制线改善了风挡局部区域的气流流动。

Conic curve is mostly used in traditional aircraft design process due to its good geometric characteristics, but its ability of shape deformation is limited to its single control parameter, while flexible shape deformation is the main characteristic of NURBS （Non Uniform Rational B-Splines） curve. According to the configuration layout and the ergonomic constraints in the aircraft design process, NURBS curves and surfaces are used to implement shape parameterization and to generate flexible geometries for the forward fuselage,where related constraints are embedded in the parametric model. Relative lengths and angles are used to describe the control points of NURBS curves, CFD analysis is performed and the parameters are optimized to gradually reach a satisfactory forward fuselage shape. In addition, a transverse control curve is added at windshield area to further improve the local airflow. The results indicate that： it is a rapid and convenient way to obtain a desired shape by combination of the methods of NURBS and CFD; it＇s more flexible to control shape. Adding transverse control curve can imorove the local airflow at the windshield area.