Theoretic model of flow resistance for gas-filled accumulators in liquid rockets

Hydraulic dynamics analysis of the pressurized supply system is needed in the process of longitudinal structure stability analysis of the launch vehicle. The method of calculating the accumulator’s resistance directly affects the accuracy of the dynamic analysis of the supply system. At present, the commonly used method is to ignore the influence of the fluid flow inside the propellant supply system and to analyze the accumulator resistance with an orifice flow model. However, this method has large errors. In this paper, by introducing the communication port flow model, the non-linear resistance calculation formula of the accumulator is deduced, where the influence of the vertical flow in the propellant supply system is considered. Then, this theoretical calculation method is verified by conducting a steady-state simulation on an accumulator. Under the various situations, it is discovered that the nonlinear resistance calculation approach suggested in this study may greatly increase prediction accuracy within a variation of less than 10%, whereas predictions based on the orifice flow model have deviations above 30%. The linear resistance theoretical formula under quasi-steady condition is further deduced and the linear resistance curve is drawn. The linear resistance of the accumulator was found to have a minimum value, which is related to the total flow area of the communication port and the velocity of propellant inside the main pipe.