Study on rigid–liquid coupling dynamics of liquid rocket cold ejection process

To address the risk of attitude instability caused by the strong coupling between propellant sloshing and rocket body motion during the cold ejection process of liquid rockets, this paper conducts a systematic study on the rigid–liquid coupling dynamics of the cold ejection process. First, combined with the structural parameters of the Long March 2C rocket, a multi-body dynamic model of the rocket body considering contact collision, ejection force loading, and other factors is established. A propellant sloshing model is constructed using the Moving Particle Semi-implicit (MPS) method, and a bidirectional coupling simulation interface is built to realize rigid–liquid strong coupling simulation. Second, the effectiveness of the modeling method is verified through the MPS method example validation, with the relative error between the simulation results and NASA experimental data ≤1.23%. Subsequently, the influence laws of thrust eccentricity angle and guide rail-adapter clearance on orbital exit performance and attitude stability are quantitatively analyzed. Finally, the optimization range of key parameters and engineering technical measures is proposed. The research shows that the thrust eccentricity angle is the core parameter affecting cold ejection performance, and the attitude stability is optimal when the eccentricity angle ≤0.25°. The guide rail clearance is recommended to be controlled within 0.5–1.0 mm to balance assembly tolerance and stability. The rigid–liquid coupling simulation method established and the nonlinear coupling mechanism revealed in this paper provide a scientific basis for the design optimization of liquid rocket cold ejection systems and have important theoretical significance and engineering application value.