The Modeling And Characteristics Analisis Of Over/under TBCC

Turbine-based combined cycle engine has become the most promising first stage power system because of its self-launching, big Mach range access and reusability, etc. For the over-under TBCC engine, the two engines work in independent duct which makes it more controllable and it’s become the main study object. This thesis studied the change rules of the characteristics of over-under TBCC engine and the control laws.Firstly, the turbojet model, ramjet model and transition model were built according to the three modes of over-under TBCC engine along the flight envelope. For the turbojet mode, the turbojet model was built based on the composition models of turbojet. For the ramjet mode, the ramjet model was built based on the three modes of ramjet: scramjet mode, ramjet mode and inlet unstart. For the transition mode, the transition model was built based on the changes of the inlet area of the two engines.Then, the characteristics of the combined engine during the three modes along the flight envelope was simulated and analyzed. During the turbojet mode, the change rules of the surge margin, pressure ratio of compressor, the thrust of turbojet, the fuel mass flow along with the changes of the turbine speed, the nozzle throat area and the afterburner working ways. During the ramjet mode, the spatial distribution of fuel equivalence ratio, inlet throat ratio and inlet expansion ratio of the four critical sates of mode transition and the change rules of the temperature of combustor outlet and the thrust when ramjet works in ramjet or scramjet mode along with the changes of fuel equivalence ratio, inlet throat ratio and inlet expansion ratio was simulated and analyzed. During the transition mode, the change rules of the characteristics of turbojet along with the change of the inlet area was simulated and analyzed.Finally, according to the analysis result above, a model state parameters database was built with the engine model. And the control laws for the three modes of combined engine was obtained for the designed thrust change rule under certain constraint conditions along the flight envelope with the database. So did the characteristics change rules under the control laws. And tested combine engine model with the control laws.