| Airbreathing hypersonics studies the technology of aerospace vehicles propelled by airbreathing engine or combined cycle engine for long-distance hypersonic flight in atmosphere layer or trans-atmosphere layer at flight Mach number above 5. Its core is scramjet and airframe/propulsion integrated vehicle.With the development of computer technology and numerical methods, numerical methods have been extensively used to design the combustor of scramjet. With ground test and flight test, computational fluid dynamics (CFD) has become one of the three primary means of scramjet research, playing a more important role.For numerical simulation of hydrocarbon fueled scramjet, in order to obtain accurate combustion details and flow field characteristics of combustor, and thoroughly investigate the effects of some important species, such as the vitiation of incoming flow on the engine's performance, it is necessary to use detailed chemical reaction kinetic model capable of accurately describing the characteristics of ignition and combustion of the fuel. However, such models for hydrocarbon fuel are usually very complicated, with up to a hundred species and thousands of reaction steps. For the present time, it is difficult to apply those models directly in 3D simulation of combustor. Therefore, to solve the difficulty, this paper carries out research in three aspects.Firstly, from the aspect of numerical method, the approach of in situ adaptive tabulation (ISAT) is adopted to speed up chemical reaction calculation and increase is efficiency. The paper introduces in detail the basic principle of the approach. On the basis of this, the software DOS-ISAT (Data Operation Software using In Situ Adaptive Tabulation) is developed with new way of data parallization. The software is coupled with the large scale, 3D parallel software AHL3D of the author's research group. With AHL3D, using current global reaction model of kerosene with 10 species and 12 reactions, it is carried out with SW MPP parallel cluster of 1024 CPUs to simulate CARDC's 1m model scramjet. The paper analyzes the computational results and compares them with experimental results, giving detailed 3D flow structure of the whole engine and analyzing its performance.Secondly, from the aspect of chemical reaction kinetic model, the paper uses mathematic method to reduce the detailed model, obtaining a reduced reaction model with less calculation. At first, with reference to domestic and abroad chemical reaction models of kerosene, the paper establishes a model with 109 species and 946 reactions. Then, the software SPARCK, specifically developed for chemical reaction kinetic model reduction is applied to reduce the model, reaching a reduced model with 22 species and 18 global reactions. Through calculating the delay time of kerosene ignition and numerical simulation of pre-mixed kerosene flame under one atmosphere, the paper verifies and validates the accuracy and the efficiency of the reduced model.Finally, the obtained reduced model and the DOS-ISAT/AHL3D software are used to do 2D simulation of a practical 1m model scramjet. The paper analyzes the results and compares them with experimental results, showing that the reduced model could pretty well simulate the complex kerosene combustion process in scramjet with high accuracy and practicability. At the same time, the whole process opens a new feasible way of applying reduced model for kerosene reaction from theoretical research to practical scramjet simulation.This paper consists of five chapters. Chapter 1 gives a brief introduction of the background of scramjet research. It analyzes the difficulties and the current situation of hydrocarbon fueled scramjet simulation both at home and abroad. Then, it gives a review of research on detailed and reduced chemical kinetic mechanisms for hydrocarbon fuel. Thirdly, it introduces the current situation of the research and the application of ISAT both at home and abroad. Finally, the main works of the paper is presented.Chapter 2 introduces the control equations, numerical methods, chemical models, physical models and numerical schemes used in calculations. It gives detailed description of the ISAT technique and its principle, and the parallel software DOS-ISAT. The software is successfully coupled with the large scale, 3D parallel software AHL3D. In order to verify the method and the software, five examples of supersonic combustion are simulated. Comparing the numerical results with the experimental ones, it indicates that the method's accuracy is comparable to the approach of direct integration, and the results are accurate and reliable. Compared with conventional method of direct integration, the software increases the general speed of calculating chemical reaction terms by 2 to 3 times, dramatically improving the efficiency. Additionally, primary numerical results show that DOS-ISAT has a very good parallel efficiency.Chapter 3 is about the massive parallel 3D numerical simulation of kerosene-fueled scramjet. With DOS-ISAT/AHL3D, using current global reaction model of kerosene with 10 species and 12 reactions, it is carried out with SW MPP parallel cluster of 1024 CPUs to simulate CARDC's 1m model scramjet. It compares in detail the calculated wall pressure with the value measured in experiment, giving detailed 3D flow structure of the whole engine and analyzing thoroughly its performance. The numerical results also prove the feasibility of applying DOS-ISAT in large scale parallel system. Compared with the conventional method of direct integration, the software improves remarkably the calculating efficiency of chemical reaction, nearly reducing the CPU time for calculating chemical reaction by half.Chapter 4 introduces the paper's research on chemical kinetics of kerosene. Firstly, on the basis of domestic and abroad research, it puts forward a surrogate model with mole ratio of 79% of n-decane, 13% of trimethylcyclohexaneclohexane and 8% of n-ethylbenzene, establishing a detailed model for kerosene with 109 species and 946 reactions. Then, using the software SPARCK specifically developed for chemical reaction kinetics reduction, a reduced model with 22 species and 18 global reactions is achieved. Finally, using both detailed and reduced models, the paper calculates the ignition delay time of kerosene and compares the results with experiments, verifying the reliability of the model. It also simulates the pre-mixed kerosene flame under one atmosphere, and compares the results with references and experiments. The comparison shows that the reduced model of the paper could accurately give the flow's combustion characteristics, and therefore could be used to simulate kerosene combustion.In addition, with the DOS-ISAT/AHL3D software, the paper simulates the practical 1m model scramjet using the reduced model with 22 species and 18 global reactions and the current global reaction model with 10 species and 12 reactions, to compare the results of the two models. The results show that the distribution of wall pressure using reduced model agrees well with the experimental measurements. Compared with the global reaction model, the distribution of pressure in the cavity using the reduced model is nearer to experimental results. The results of pressure distributions of the two models on other parts are nearly the same. Generally, the reduced model can simulate well the complex combustion phenomena in a kerosene-fueled scramjet. The model has high accuracy and practicability.Chapter 5 is the conclusions, including the achievements and the innovative points of the paper. It also gives the outlook of future work.
|
PDF Full Text Request