【作者】 王兰；

【导师】 乐嘉陵；

【作者基本信息】 中国空气动力研究与发展中心 ， 流体力学， 2007， 博士

【摘要】 超声速燃烧冲压发动机简称超燃冲压发动机(Scramjet),采用与机身一体化的设计,主要用在高空大气层内Ma>6飞行的吸气式高超声速飞行器上。超燃冲压发动机燃烧室内流场有超声速燃烧、激波与边界层相互作用等复杂现象。作为重要的研究手段之一,计算流体力学(CFD)能很快得到流场细节,尤其是在初始设计阶段,CFD能为发动机选型提供依据。然而,随着飞行器外形的复杂化,生成结构网格越来越困难,费时费力的网格生成成为了设计阶段的瓶颈。非结构网格节点间没有结构性限制,网格的大小和疏密很容易控制,一旦外形确定,可以快速地自动生成网格;另一方面,非结构网格随机的数据结构在进行网格自适应和并行处理时很方便。由于不像结构网格网格邻点是显而易见的,非结构网格必须将网格点的相关性等信息存储下来,因此更耗内存,一些数值算法如LU方法不能直接用于非结构网格CFD计算。现在许多在结构网格上发展成熟的方法逐渐成功地应用到非结构网格中,非结构网格技术广泛地用于各种流动的数值模拟,但国内还没有见到用自己开发的非结构网格计算软件并行求解超燃冲压发动机的复杂燃烧流场。本文围绕超燃冲压发动机反应流场的研究,在国内首次基于非结构网格发展了一套适用于超声速湍流反应流数值模拟的大规模并行计算CFD软件平台AHL_UNS3D。在对程序进行了大量的算例验证后,对超燃冲压发动机内部流场开展了细致深入的数值模拟研究。为了更准确地模拟超燃冲压发动机燃烧室内的湍流流场,壁面附近采用六面体网格或垂直于壁面“长出”的三棱柱“半结构”网格,其余地方采用四面体网格,金字塔形网格用来连接不同形状的网格单元。AHL_UNS3D基于MPI实现并行,采用格点有限体积法离散积分形式的控制方程,能够模拟完全气体和多组分混合气体的二维、轴对称、三维的定常和非定常的无粘流、层流和湍流。时间推进采用显式Runge-Kutta法或LU-SGS方法,无粘通量计算有Steger-Warming、Van Leer、AUSMDV和AUSMPW+四种格式。有多种氢气反应和碳氢燃料乙烯反应的化学动力学模型,有S-A一方程湍流模型和k-ω两方程湍流模型(包括原始的Wilcox k-ω、Kok TNT、Menter BSL和SST)等多种湍流模型,两方程模型可与流动控制方程耦合或解耦求解。采用14个定常流和2个非定常流算例考核AHL_UNS3D模拟无粘流、层流、湍流、多组分化学反应流动和非定常流动的能力,证明该软件平台具有较高的计算精度和可靠性。针对超燃冲压发动机燃烧室内流场的特点,选取了Lehr球头激波诱导燃烧、凹槽、压缩拐角和三维圆孔垂直喷氢等多种典型流动,通过和实验值的比较,选择了适合超燃冲压发动机反应流场的化学动力学模型、无粘通量的计算格式和湍流模型。为验证AHL_UNS3D对超燃冲压发动机化学反应流场的模拟能力,对经典验证例子,即Burrows & Kurkov的二维氢气顺喷的扩散和燃烧两种流动进行了数值模拟;接着对以氢气为燃料的澳大利亚昆士兰大学高超声速技术中心Hyshot计划的地面实验超燃冲压发动机、日本国家航空与航天实验室(NAL)的双模态燃烧室模型分别进行了二维和三维片式数值模拟,并应用到了气动中心的氢燃料超燃冲压发动机整机冷流和三种当量油气比的燃烧流场三维数值模拟中,最后模拟了半宽度Taha燃烧室无引导乙烯的反应流,分析了凹槽对乙烯点火及燃烧的作用。本文共分为七章。第一章为引言,简要介绍研究背景和超燃冲压发动机的国内外研究现状;介绍了非结构网格的特点、发展和国外超燃冲压发动机非结构网格数值模拟软件的功能及应用,并从七个方面与本文开发的软件AHL_UNS3D进行了比较;最后简要介绍了本文的主要工作。第二章为计算方法,主要介绍软件所用的数据结构和控制体、控制方程、湍流模型、方程离散方法、无粘通量计算格式和并行算法。第三章是算例验证,第四章、第五章和第六章是氢或碳氢燃料超燃冲压发动机燃烧室及整机数值模拟。第七章为结束语,阐述了论文的主要成果和创新点,并对软件未来的发展进行了展望。更多还原

【Abstract】 Supersonic Combustion Ramjet (Scramjet for short) is integrated with the airbreathing hypersonic vehicle which aims mainly for the flight in the high altitude environment at Mach number above 6.0. There are complex phenomena such as supersonic combustion and the interactions between the shock and the boundary layer in the internal flowfield of the Scramjet combustor. As one of the important research methods, Computaional Fluid Dynamics(CFD) can get the detail of the flowfield in a short time and it can offer the basis for the choice of an appropriate engine configuration especially in the process of the preliminary design.However, it has become more difficult to generate the structured grid when the geometry of the vehicle is more complex, so the design process has been bottlenecked by the time consuming and laborious generation of the grid. Freed from the structural limitation, it is much easier for the unstructured grid to control the size and the density of the mesh and the generation of the unstructured grid can be finished quickly and automatically once the geometry is determined. On the other hand, the data structure of the unstructured grid provides convenience to the adaptation of the grid and the parallelization. Unlike the structured grid, the neighbor points of the unstructured grid are not explicitly known, so the information about the connectivity of the grid etc must be recorded in the preprocessing process and it results in more memory taken than the structured grid. Some numerical methods such as LU decomposition can not be applied directly to the CFD computation on the unstructured grid. Now many technologies which have been maturely developed on the structured grid have been successfully used in the unstructured grid and the unstructured grid technology has wide applications in all kinds of flow simulations, but up to now there is scarcely any literature about the parallel simulations of the complex combustion flowfield of the Scramjet combustor by the independently developed numerical software on the unstructured grid at home.A numerical software platform applicable to the supersonic turbulently reacting flow simulation named AHL_UNS3D has been developed by the Airbreathing Hypersonic Laboratory of CARDC on unstructured grids focusing on the research of the Scramjet reacting flow. After a lot of verifications and validations, numerical simulations have been conducted on the internal flowfields of the Scramjet.To simulate the turbulent flow of the Scramjet combustor more correctly, the hexahedral or prismatic semi-structured grid is extruded perpendicularly from the wall and tetrahedral grid are used for the rest space. Different kinds of grids are connected by the pyramidal grid.AHL_UNS3D achieves parallelization based on MPI and discretizes the integral governing equations by the cell-vertex finite volume method. It can simulate two-dimensional(2D), axisymmetrical and three-dimensional(3D) steady and unsteady invicid, laminar and turbulent flows of the perfect gas and the multispecies mixture. The time evolution can use Runge-Kutta or LU-SGS method. Four schemes including those of Steger-Warming、Van Leer、AUSMDV and AUSMPW+ can be used for the inviscid flux vector calculation. There are several chemical kinetic models for the hydrogen or the hydrocarbon fuel ethylene and there are two types of turbulence models: Spalart-Allmara(S-A) one-equation turbulence model and k-ωtype two-equation turbulence models (including the original Wilcox k-ω, Kok’s TNT, Menter’s BSL and SST), and the two-equation turbulence models can be solved coupled or uncoupled with the main govening equations.14 steady and 2 unsteady benchmark cases are simulated to validate the capabilities of AHL_UNS3D for the inviscid, laminar, turbulent, multispecies chemically reacting flows and unsteady flows and the results indicate that the numerical software has good resolution and reliability. Considering the characteristics of the internal flow of the Scramjet combustor, typical flows such as Lehr’s shock induced combustion, the cavity flow, the compression corner flow and the perpendicular injection flow of the hydrogen from a circular hole are calculated and the appropriate chemical kinetic model, numerical scheme for the inviscid flux computation and turbulence model are chosen for the reacting flow of the Scramjet by the comparisons with the experimental results.To validate the ability of AHL_UNS3D for the chemically reacting flow of the Scramjet, the diffusing and reacting cases of the 2D parallel injection of a well known benchmark, ie. the hydrogen flow of Burrows & Kurkov are simulated. 2D and 3D jet-to-jet simulations are conducted respectively for the Scramjet models of the Hyshot scheme of the hypersonic center of Queesland University of Australia and the National Aerospace Laboratory(NAL) of Japan. Then the numerical simulations for the cold flow and reacting flows of three fuel/air equivalence ratios of a whole Scramjet engine of CARDC fueled by the hydrogen in slice region are conducted. Finally the reacting flow of Taha’s combustor without the piloted ethylene in the half-width region is simulated and the influence of the cavity to the ignition and combustion of the ethylene is analyzed.This paper consists of seven chapters.Chapter one is the introduction. The background of this paper and the status of the researches of the Scramjet at home and abroad, the characteristics and the development of the unstructured grid technology, the functions as well as applications of numerical softwares abroad able to simulate the Scramjet flowfield on unstructured grids are introduced and comparisons in seven different aspects with AHL_UNS3D are made. Finally, the main work of this paper is outlined briefly. Chapter two is about numerical methods, including the data structure and the control volume, governing equations, turbulence models, the discretization method of the integral governing equations, numerical schemes for the inviscid flux computation and parallel algorithms used in the software. Chapter three is validations of the numerical software. Chapter four to six are the simulations of the flowfields of the Scramjet combustor and the whole engine fueled by the hydrogen or the ethylene. Chapter seven is the conclusion. The main researches and innovative points are reviewed and the outlook of the future development of the software is given.更多还原