Study On Dynamic Characteristics And Modeling Of RBCC Engine

RBCC engine combines the advantages of rocket and ramjet engine, and can work with good performance over the full operating envelope, which has a widely application prospect. Currently the mechanism of flow and combustion and the combustion organization technology has been much explored. As research continues, RBCC engine has reached the engineering application stage. We must control the engine effectively to make sure it can work safely and reliably in full-model conditions. Besides, to research in the dynamics of engine's Aerothermo process and to establish the control model is also a must.In this paper, we study the dynamic characteristics of RBCC engine through three-dimensional CFD techniques and obtain the dynamic response data by changing the equivalence ratios of secondary fuel and switching the location of injection. With the study of dynamic characteristics of thermal throat form and discussion of the principle to select state variable, we determine the position of the characteristics of cross-sectional area. Based on the direct-connected experiment of RBCC engines, we study the dynamic characteristics of time, the rules of heat release, and the transition and organization of shock. The form of state space model has also been determined through direct-connected experiment and numerical simulation. Based on the CFD simulation results of Ma3, we establish a two-dimensional state space model by fitting method and the genetic algorithm, discuss the impact of model accuracy with number of feature data points and the matched relationship between the model parameters, and determine the controllability and the observability of state space model.On the basis of studies mentioned above, the main conclusions we obtained in this paper include following three aspects:Firstly, the feature section we select should be closed to the thermal throat, so that the operating parameters of feature section can change with the engine more sensitively. The location of the cavity is concentrated heat zone and it promotes the generation of thermal throat a lot, so we select the section after cavity as the feature section.Secondly, the method of fuel injection and the Mach number can affect the response time of RBCC engine. With the same the injection position, the equivalence ratios of secondary fuel injection is higher, the time of dynamic response is longer. With the same equivalence ratios of fuel injection, the response time of grading injection is longer than that of concentrated injection; with the inflow Mach becomes higher, the dynamic response time gradually becomes shorter.Thirdly, based on the dynamic data gotten in step experiment of secondary injection, we can use both fitting method and genetic algorithms to establish a state-space model. Compared with fitting method, genetic algorithm has broader scope of application. Taking both model accuracy and computational efficiency into consideration, we should select 20 points. Furthermore, when using Genetic algorithm, the parameters of genetic operators should match with the range of population.