Dynamic interaction between clustered liquid propellant rocket engines under their asynchronous start-ups

Sergey I. Dolgopolov, Olexiy D. Nikolayev ^*, Nataliia V. Khoriak

Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine, 15, Leshko-Popel Str. Dnepr 49600, Ukraine

Abstract: A nonlinear mathematical model of the low-frequency dynamics of the clustered multi-engine rocket propulsion system has been developed and the computations of the engine transient processes during the start-ups of the four-engine propulsion system with a shared feed system have been made applied. Based on propulsion system start-up modeling the influence of the connectivity of engines in a cluster on the starting characteristics of individual engines is shown. In particular, an advanced nonlinear mathematical model of the pump cavitation phenomena is a distinctive feature of the mathematical model. The computation results showed that the asynchronous engines start-ups during rocket lift-off lead to severely nonlinear engine transients and clustered engine thrust misbalance. The influence of the rocket engines asynchronous start-ups on the clustered feed system transients depends on many factors, mainly on from the clustered feed system low-frequency dynamics, the magnitude of the disturbance and the phase difference between disturbances acting on different branches of the feed system. The deep lingering dips in the flow rate and pressure transients are possible due to the nonlinear dynamic interaction of the engines. In case of great pressure dips at the pump inlet (up to the pressure of saturated vapors during significant periods of start-up time) the cavitation breakdowns of the pumps of one or more engines from the cluster are possible. This can disrupt the operation of the entire propulsion system and leads to the failure of the launch vehicle mission.

Keywords: Liquid propellant rocket engine; Clustered engine thrust misbalance; Nonlinear mathematical model; Start-up transient; Pump cavitation model; Low-frequency processes; Start-up sequence; Shared feed system

https://doi.org/10.1016/j.jppr.2021.12.001