Study On Modeling And Simulation Of Liquid Rocket Engine Built With Modelica Language

Liquid rocket engine is a complex thermal fluid system which consists of different disciplines such as flow,combustion,heat transfer and chemical reaction and so on.Multi-domain has become an important feature of modern rocket engine.However,the current modeling and simulation researches of engine are rarely focus on multi-domain and whole-system with the expansibility and compatibility to be further improved,thus it is difficult to consider relations between the different components and fields.Modelica is a kind of popular modeling language in multi-domain physical system having been widely used in many complex systems.In this paper,a general and modular simulation library of liquid rocket engine is developed based on Modelica language.Then dynamic simulations for the start-up process of LOX/Methane rocket engine and working process of LOX/LH2 rocket engine in failure scenarios are taken out.First,the dynamic mathematical models of typical components of liquid rocket engine are established.As for turbo pump,a model of centrifugal pump is built with Suter expressions without the calculation problem at zero rotating speed and non-zero mass flow.The polynomial with zero intercept is used in the equation of turbine efficiency,which is helpful for the calculation at zero rotating speed.In rotor model,the influences of friction torque are considered.Besides,a modified Bartz equation taking account the effects of combustion zone distribution,thickness variation of the boundary layer and flow acceleration in nozzle is introduced in the model of thrust chamber.According to the dynamic mathematical models of those components,a general and extensible simulation library include fluid physical properties,turbine pump,thrust chamber and so on,is established on OpenModelica software using the method of "top-down system decomposition and bottom-up system build".Based on the module library,simulation models are established for the LOX/Methane thrust chamber experiment.The simulation results match with the testing data very well and the accuracy of the models are validated.Then the dynamic simulation models for the whole system of LOX/Methane rocket engine are built to simulate the start-up process.The influences of the opening size of oxygen valve,the start time from start-up to main stage and starting friction torque on the start-up process of the engine are studied.Some advices for the adjustment of start-up schedule are discussed.In addition,simulation models are also established for LOX/LH2 oxygen turbine clogging experiment and the simulation results match very well with the testing data.Through the simulation of whole system LOX/LH2 engine with oxygen turbine clogging,the changes of main parameters under different clogging degrees are analyzed.