Simulations of cryogen expulsion from a space depot under zero gravity

Abstract

With an increasing number of missions in space, cryogenic fluid supply systems become necessary as mission duration is extended. Most of the system operations involve multiple-phase phenomena. Accurate simulation of the operations is needed to predict the physics and efficiency of these systems. One operation of interest is the expulsion of liquid cryogens from a partially filled depot; the challenge concerns finding ways to expel the liquid while preventing vapour from entering the transfer line. The problem involves tracking the motion of a floating, mobile and expanding vapour ullage as fluid is expelled from a tank. The simulation of the interface movement of the vapour ullage in a volume of confined liquid under zero gravity is carried out by solving the Navier-Stokes equations in the transformed boundary-fitted curvilinear co-ordinate system using a finite difference approach. An alternating expulsion and pressurization scheme is presented for the operation based on mass and momentum conservation.