Numerical Investigation of Cryogenic LH2 Tank Pressurization in Callisto

Abstract

Cryogenic fluid management is becoming increasingly important with the novel challenges that RLVs pose onto launchers. Especially transitions between high and low thrust, long coasting phases at low fill levels and a higher proportion of non-axial thrust induce complex flows within the propellant tanks. Within the framework of the CALLISTO-project, which is a joint effort of JAXA, CNES and DLR to develop a functional vertical take-off vertical landing (VTVL) prototype, DLR is developing the hydrogen tank. This paper presents the numerical approach to simulate the pressurization fluid behavior in order to predict pressurant budgets and thermal residuals. Numerical modelling of these internal flows incorporates multiple challenges including phase change at the liquid-gas interface, which is highly dependent on the ullage flows. For this task, simulations are performed with OpenFOAM using the dedicated TwoPhaseFlow library, which allows modeling of multiple phases, multiple species, phase change, conjugate heat transfer and includes gravity models which allow for micro-gravity interface prediction. In the presented approach, the diffusor flow and the multiphase simulation of the internal tank flow during the trajectory are solved independently and coupled with a new flexible spherical boundary condition to allow for faster and more flexible development iterations.