Modeling spray-bar pressure control of a large-scale liquid-hydrogen propellant tank in normal gravity

A two-phase Eulerian–Lagrangian CFD framework was developed and validated for simulating spray-bar pressure control in the Multipurpose Hydrogen Test Bed (MHTB) liquid hydrogen tank at a 25% fill level. Simulations were conducted for three configurations: a quarter-tank sector with symmetry planes, a full tank with a centrally located spray-bar, and a full tank with an experimentally accurate off-center spray-bar. The model couples a volume-of-fluid (VOF) approach with an in-house T-sat droplet sub-model that accounts for breakup, coalescence, and heat and mass transfer to the ullage vapor. All cases accurately reproduced the experimentally measured pressure reduction and ullage temperature decay during the 35-s spray cycle. The quarter-sector simulation closely matched the full-tank results while reducing computational time from weeks to days, indicating its suitability for rapid system-level studies. The full-tank representation remains necessary only when detailed ullage temperature distributions or asymmetries must be resolved. The validated framework offers a computationally efficient tool for evaluating spray-bar design parameters and supporting the development of future cryogenic fluid management systems for spaceflight applications.