Calculation and analysis by modular modeling for frequency characteristics of a LOX/LH₂ rocket engine

In order to analyze the frequency characteristics of a LOX/LH₂ rocket engine，an engine linearized dynamic model with main and subsidiary systems coupled was developed，including pipelines described by one-dimensional distributed parameter model，combustion components described by adiabatic flow model considering entropy wave and pumps components were described by model considering cavitation.The transcendental functions in thermodynamic component models and distributed parameter models were expressed by rational approximation.After establishing modular simulation model in Simulink，a frequency sweep was conducted to obtain the frequency characteristics，and hot test data was implemented in validation.The result showed that the modular simulation library is user-friendly，and is capable of analyzing the low to medium frequency characteristics of the engine system.Under the excitation of gas pulsation，the engine produced the frequency response of 10 and 165 Hz in main system and 124 and 204 Hz in subsidiary system.The calculated characteristics frequency showed better accuracy while considering the rotation speed feedback.The stability of the engine system was improved while increasing the local resistance of the pipeline before the pump or increasing the pressure drop of the gas generator injection.