Resolving breakup in flash atomization conditions using DNS

Abstract

Flash boiling can occur in rocket thrusters operating in the vacuum of space when cryogenic propellants are injected into the reaction chamber that is initially at low pressure. The dynamics of this process will determine the spray breakup that will then drastically affect the mixing of fuel and oxidizer, the reliability of the ignition and the subsequent combustion process. A multiphase solver with interface capturing is used to perform direct numerical simulations (DNS) of the primary breakup of the liquid oxygen jet that is driven by homogeneous nucleation, growth, coalescence and bursting of vapour bubbles in the superheated liquid. Considering the main breakup patterns and droplet formation mechanisms for a range of conditions, we evaluate the effectiveness of the volume of fluid (VoF) with continuum surface stress (CSS) method to capture the breakup of thin lamellae formed at high Weber numbers. A grid refinement study shows convergence of the mass averaged droplet size towards a droplet diameter. The order of magnitude of the resulting diameter can be estimated based on the thermodynamic conditions.