| Due to its extremely high military application value,the hypersonic technology is becoming the focus of development in aerospace field.For the hypersonic technology,the propulsion technology is the key part of that technology.It is very important to investigate the factors that influence the and mixing and combustion of fuel in the scramjet engine and the way to conduct a steady and efficient mode transition.First of all,the theses introduces the reasons why the fuel mixing efficiencies in the scramjet engine should be investigated,and the common strategies used until now.The methods such as wall injection,struts and cavities are introduced in detail.The definition and classification of the combustion mode technology are also introduced,and some of the mode transition phenomenon,and the hysteresis phenomenon during the transition are described as well.Then,based on the numerical theory used in this theses,the flow and combustion controlling equations,engineering turbulence model and related chemical reaction models are briefly introduced.The definition and applicable values of relevant parameters are given,which provides a foothold for simulation after.The second chapter also compares the predicted results with the available experimental data in the open literature,and predicted results obtained by two models are compared as well,namely RNG k-? and SST k-?.The results show that the RNG k-? model can get more accurate results for this example.Compared with the experimental results,the comparison shows that the turbulence models and boundary conditions used in this theses can accurately capture the structural characteristics of the flow field and can also obtain believable parameters in the flow field,such as pressure and temperature.The effects of the combination parameters between strut and cavities(including the aspect ratio of the cavity,the cavity trailing edge angle,the relative distance between the cavity and the strut)and the wall injection pressure on the structure and performance of the flow field are studied by numerical simulation.By comparing the flow field structure(Mach number contour and density contour),the mass fraction distributions of different components in the flow field and the mixing efficiency,combustion efficiency,one-dimensional average Mach number,total pressure recovery coefficient along x-axis,the influence law of wall injection pressure on the overall performance of the combustor is analyzed.Also,the appropriate flow parameters for the mode transition are obtained.The hysteresis phenomenon during the mode transition is studied by numerical simulation.By changing the injection pressure ratio of the fuel,the engine mode transition is simulated in the strut-based combustor.The hysteresis effect in the mode transition is confirmed by observing the variations of wall static pressure,Mach number along the combustor and the flow field structure.Then,the mode transition is conducted in the combustor based on the strut-cavity combination,and the effect of the cavity on the mode transition is obtained;finally,the variation rate of injection pressure is changed,and the effect of the injection pressure variation rate is analyzed.Through the numerical simulation of the three-dimensional scramjet model,the theses finally carries out a more detailed analysis of the mode transition process.The analysis is divided into two processes,namely scramjet-ramjet transition and ramjet-scramjet transition.The changes of wall pressure and Mach number during the transition process are analyzed respectively.The Mach number and temperature distribution of the flow field are analyzed.The internal mechanism during the mode transition is elaborated.In summary,this theses firstly analyzes the performance of the combustor when the fuel is injected through both strut and walls and when the strut is combined with cavities.Then,the influencing factors of the mode transition process are analyzed.Finally,the intrinsic mechanism of the mode transition is investigated. |
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