Numerical Study on Working Process of Gas-filled Accumulator

Gas-filled accumulator is the key technology of oxygen pressurization system, which has successfully achieved pogo stabilization in several launch vehicles. Previous research on the gas-filled accumulator relies a lot on the lumped parameters method, where many factors need to be simplified in the process of modeling and analysis. In this research, a computational fluid dynamics model, based on Navier-Stokes equation and RNG $k-\varepsilon$ model, is established for simulation research on a simplified gas-filled accumulator injecting with gaseous oxygen. Volume of Fluid method is used to track the volume fraction for liquid oxygen free-surface inside the accumulator, where the gaseous phase is regarded ideal and the liquid phase is considered incompressible. The accumulator worked for 10s under oscillating pressure with an amplitude of 0.1 MPa and a frequency of 10 Hz, while the ullage has four different working conditions. The result shows that there will be a periodic fluctuation of liquid level inside the accumulator if the flow difference of injection and exhaust gaseous oxygen flow rate is not large enough. But excessive flow difference will cause the reduction of ullage volume, thus reducing the accumulator compliance. And without any liquid management method, the propellant inside the accumulator will splash, resulting gas babbles being mixed with the propellant, and sucked into communication ports periodically due to the vortex inside the liquid domain. The simulation result also indicate that the vertical flow of the mainstream will compress the flow area of communication ports, causing the linear resistance of the accumulator to be larger than the estimated value of the orifice flow model. This study provides a research reference for the design and application of gas-filled accumulator.