| The operation of variable thrust liquid rocket engine always includes starting,shutting down and switching between different working conditions.It is of great significance to study the influence of switching conditions on engine heat transfer characteristics and system frequency response characteristics.This paper takes a certain type of variable thrust liquid rocket engine as the research object,selects two typical working conditions and adopts the method of numerical simulation to study and compare the heat transfer characteristics of regenerative cooling thrust chamber and the dynamic characteristics of the whole system under two working conditions.Considering that the propellant supply system and the thrust chamber are connected,which means the inlet boundary condition of the thrust chamber is the outlet condition of the propellant supply system.The flow field results of the thrust chamber and the results of the whole system simulation have a mutual correction effect,making the simulation results obtained in this paper more credible.Therefore,this article uses the structure as below.The main research contents of this paper are as follows:The combustion and nozzle flow of the thrust chamber with fuel and oxidant segment-cooling structure are numerically simulated,and fluid-solid coupling method was adopt to calculate the heat flow between the airflow in the thrust chamber and the solid wall and the coolant.The axial distributions of temperature and heat flux on the inner and outer walls were extracted.A gas generator cycle liquid rocket engine simulation model was established based on module built on the finite element method of the segmentation concentration parameter.The module of the engine was built by the second-development function of commercial software AMESim,including centrifugal pump,turbine,mixed ratio regulator,gas generator,etc.The time domain simulation of the engine system is carried out to study the act of main parameters of each component under start-up and variable working conditions.Effect of delayed start on four parallel thrust chambers is analyzed.For the phenomenon of thrust vibration in the thrust chamber,Fourier transform method was used to transform the time-domain thrust simulation results to the spectrum diagram,for analyzing the influence of spring stiffness coefficient and film shear modulus on the vibration frequency.The system characteristics and frequency response of variable thrust engine under variable working conditions are studied.By extracting main frequencies during the variable operating conditions,the frequency of the corresponding energy peak is found to be 5.34 Hz.During the transition from high operating condition to low operating condition,the inlet pressure signal with disturbance of frequency mentioned above was input,the simulation results show that this low frequency disturbance reduces the stability margin of the system and the occurrence of disturbance signals at this frequency should be avoid.Based on a large number of numerical calculations,this paper summarizes the working characteristics of the engine under different working conditions,and puts forward some problems that need to be improved at present,which lays a foundation for further research on the variable thrust characteristics of the pump-feeded gas generator cycle engine. |
