Numerical simulation of water hammer in liquid methane feedline based on two compressible fluid models

Abstract

In order to improve the capability of distributed parameter modeling for water hammer of liquid methane propellant in a staged combustion cycle engine simulation library, pipeline flow models are established based on two different compressible fluid assumptions. One is the slightly compressible fluid assumption and the other is the completely compressible fluid. For the completely compressible fluid model, the SRK equation of state is utilized to calculate the pressure rather than the internal energy fitting formula. And for slightly compressible fluid model, the pressure equation is deduced from continuity equation by introducing sound velocity equation. One-dimensional finite volume method is used so that the two models could work well with other component models of a staged combustion cycle engine simulation library which are all programmed in Modelica language. The pressure surges of the liquid methane in a system are predicted due to valve closure. The results show a principal difference of pressure surge frequencies between two models, which is caused by the different ways of calculation of pressure. In addition, a method of numerical oscillation suppression for completely compressible fluid model is proposed and a best value of oscillation suppression coefficient is given in the present paper.