基于非结构网格流场的数值模拟及喷管型面优化

【作者】 王红梅；

【导师】 杨青真；

【作者基本信息】 西北工业大学 ， 工程热物理， 2005， 硕士

【摘要】 本文采用计算流体力学方法,重点研究了二维非结构网格的生成方法和基于非结构网格的定常/非定常N-S方程求解,并简单研究了矢量喷管的型面优化,用以提高矢量喷管气动性能。 本文首先研究了二维非结构网格的生成方法,采用Delaunay三角化与阵面推进相结合的方法。网格的划分及更新采用Delaunay三角化方法,网格内部节点的生成则是基于阵面推进法的思想。 本文还编写出了基于非结构网格的二维定常/非定常流场N-S方程计算程序。对于定常求解,本文采用格心格式的有限体积法对N-S方程作空间离散,湍流模型采用计算中广泛使用Badwin-Lomax紊流模型,它是一种代数模型,不增加求解方程的数目,计算量相对较小。用四步龙格—库塔方法作显式时间推进,同时采用当地时间步长、残值光顺等加速收敛措施。对于非定常求解,为了减少计算时间,本文采用隐式双时间法,伪时间域的求解用上面所讲的定常方法进行计算。本文给出的网格生成和流场计算的结果与实验数据符合较好。 本文还研究了优化方法,对矢量喷管的型面进行了优化设计。首先对基本矢量喷管型面进行网格生成,然后采用基于N-S方程的流场计算程序来求解流场,得到推力系数、阻力系数等气动参数、并以其中某个或某些参数构成目标函数,用复合形优化方法进行了优化设计。优化程序采用复合形法,它属于直接解法,是解有约束优化问题的有效方法之一,其应用十分广泛。其特点是原理简单、方法直观、不需要计算导数,也不需要一维搜索,复合形不要求为规则图形,灵活可变,适宜处理不等式约束问题。 另外,本文用计算流体力学方法对某型火箭发动机推力室氧腔流场进行了分析研究,确定了氧腔出口截面的总、静压力分布;提出了新的氧腔均流孔板的设计思想,并依此用流场分析结果设计了新的均流板;对新设计的均流板的氧腔进行了详细分析和实验验证。分析和验证表明新设计的均流板使氧腔出口截面压力畸变降低了11.5%,从而证明了本文提出的均流板设计思想和分析方法的正确性。更多还原

【Abstract】 In this thesis a strategy applying the CFD for the generation of tetrahedral unstructured viscous grid on two-dimensional configurations has been introduced, and flow numerical simulation of steady or unsteady N-S equations under unstructured grids is researched in emphasis. In addition, a vector nozzle shape design method that couples viscous flow analysis, a complex method is described in this paper.The unstructured grids are generated by using the combination of Delaunay and advancing front techniques. Using the Dulaunay method, the grids is compartmentalized and updated. New inner nodes are created based on the concept of advancing front techniques.A computational program based on the 2-D unstructured grids is developed to solve the steady or unsteady N-S equation. The solution of steady flow employs a finite-volume method with the Badwin-Lomax turbulent model, an algebra model, which can’ t add the number of the equations and easy to solve. The 4-step Rung-Kutta scheme is adopted and the techniques of artificial dissipation, local time stepping and residual smoothing are used to increase the convergence rate. With respect of the unsteady flow, implicit dual-time stepping method is employed to reduce the calculating time, and in preudo-time region, the method of solving steady flow, as presented above, is applied. Finally, examples of grid generation and flow calculation are presented. The numerical results are in well accord with the published data, which show that the numerical solution method is correct and robust.The optimum method is studied in this paper, a vector nozzle shape design method that couples viscous flow analysis; a complex method is described additionally. The optimum program is developed by using the complex optimum method, which is an effective method to solve the restraining problem, and widely used.The optimum process is started by a base shape of vector nozzle. the unstructured grids of the vector nozzle is generated first and then the numerical flow is simulated by solving the N-S equations to gain the Aerodynamic parameters such as the coefficient of thrust force which is defined as design as the objective function, then the optimum program is executed by the Complex optimum method and the most aerodynamically favorable geometry that can be provide with the better aerodynamic performance is obtained.In this paper, the flow in the oxygen cavity of a rocket engine thrust chamber is investigated by using CFD methods, and the distribution of total and static pressure on exit of the oxygen cavity is determined. A new concept to design the orifice plate for flow uniformity in oxygen cavity is developed, and new orifice plates for flow uniformity are designed based on this concept and the results of flow characteristics. The detailed flow analysis and experiment validation is also performed, it shows that the newly designed orifice plate reduces 11.5% of pressure distortion on oxygen cavity exit, also shows that the concept and method provided in this paper are reasonable.更多还原