Numerical simulation of atomization and mixing at a gas-liquid interface

The propulsion of a discrete liquid slug from a launch tube by the high-pressure, high-temperature gas from a combustion reaction is simulated using a transient CFD model. The simulation was performed to study the effects of interfacial heat and mass transfer on the overall behavior of the launch system. The pressure of the combustion gas peaks at about 10 MPa, its temperature peaks at 2500K, and exit velocities of the multi-phase mixture exceed 100 m/s. The Volume-of-Fluid (VOF) method was used to compute volume fractions of the four individual species considered; namely atmospheric air, combustion gas, and water in both liquid and vapor phases. The evolution of the gas-liquid interface is presented at several time steps, as are several properties near the interface such as the temperature gradients and water volume fraction. Evaporation of water into the driving gas is shown to have a relatively small effect on the combustion reaction. Turbulent mixing at the gas-liquid interface, however, is shown to have significant effects on the structure of the liquid slug, especially upon its exit to the atmosphere. The behavior of the gas-liquid interface shows distinct similarities to the Rayleigh-Taylor instability observed in the experimental study of Nevmerzhitsky, et al [1].