Subsection Evolution Optimal Design Of3D High-Lift Systems For Civil Aircraft Based On Conservative Chimera Technique

Subtle improvement of the aerodynamic performance of the high-lift systems may significantly reduce the aircraft’s empty weight and improve the aerodynamic efficiency, which will directly affect the operating costs of the aircraft, so the design of the high-lift devices plays an important role during the whole aircraft design process.On the background of the current developing large civil aircraft, this thesis focused on the aerodynamic analysis and design issues of three dimensional high-lift device, which including the grid generate automation for the complex high-lift system, the flow field simulation and genetic optimization of the parameters of multi-element airfoil and three dimensional high-lift systems. The final optimized configurations, when compared to the original, show that the maximum lift coefficient CLmax is significantly improved without the cost of decreasing the lift-drag ratio L/D performance. Specifically, the following aspects of research work are included:(1) Because of the special characteristics of the low speed flow field, the rigidity of the governing equations is greatly enhanced, resulting in the convergence difficulty of calculation. In this thesis, the time derivative term of the control equation is left multiplied by Turkel preconditioning matrix. Several preconditioned time and space discrete schemes are derived in details. Studies have shown that the above approach effectively alleviates the systems’stiffness and the condition number of the control equation at low Mach number conditions which plays a role in accelerating convergence.(2) During the genetic optimization process, several components of the high lift devices just have a relative movement to the main wing, to which the chimera grids are prettily applicable. According to chimera technique, each component grid is individually generated. In this thesis, due to the special geometry character of the high-lift devices, the component grids are generated by hyperbolic equations method. For some specific complex geometry parts, such as scissor locations and wingtip faces etc., point-to-point overset grid method is adopted. Applications of the above grid generation methods to the configurations of multi-element airfoil and three dimensional high-lift devices show that the above approach can effectively reduce the complexity and difficulty to obtain the body-fitted structured grid with high mesh quality. Based on the above design ideas, grid automation generation software HLGRID3D is developed in this thesis, which is especially suitable to the complex three dimensional high-lift systems and is well used in the subsequent optimization process.(3) According to the traditional chimera grid, the global flux conservation of flow characteristics at the sub-zone interfaces cannot be guaranteed during the sub-domain flow field information exchange process. In this thesis, the global Mass Flux Conservation algorithm MFBI2is adopted and the traditional chimera is also improved to overcome the above problems. After the grids are obtained by HLGRID3D software, a self-developed preconditioning program is adopted to solve the complex flow field of several typical high-lift systems and numerical results show that the accuracy of the conservative scheme is better than the traditional chimera.(4) In order to ensure the flight security during the landing and taking-off period, the maximum lift coefficient CLmax of the configuration should be maximized under various constrains. In this thesis, the lift coefficient at high attack angle is sub sectional genetic optimized, without trimming the lift-drag ratio performance. To improve the optimization efficiency, meanwhile, overcome the Hamming cliff problem encountered in the standard genetic optimization problems, the subsection evolution genetic optimization method is employed. Combined with the conservative chimera techniques and HLGRID3D grid generation software, the configuration parameters of multi-element airfoil and three dimensional high-lift systems are genetic optimized. As a result, the maximum lift coefficient of the final optimized geometries, compared with the initial one, is significantly improved.