A transient, two-dimensional computational fluid dynamics model is used to simulate the flow of a liquid slug through a pipe at high velocities. The slug is driven by a gas which enters the system at a constant pressure of 10 MPa. The gas accelerates the slug from rest through a distance of about 45 cm, after which the slug discharges into the open atmosphere. The interface between the two phases is initially uniform and flat, however as the flow develops, significant interphase mixing and deformation of the interface occurs.
The simulation is ultimately used to predict the velocity and dispersion pattern of the liquid slug upon discharge into the atmosphere. The gas pressure and dispersion pattern over time are compared to experimental data collected via high-speed cinematography and piezoelectric pressure gauges. The numerical model predicts a slug exit velocity of 108 m/s which agrees reasonably well with empirical measurements. However, the numerical model fails to accurately predict the structure of the dispersion pattern of the exiting liquid, specifically in terms of the amount of mixing between the liquid and gas phases. To address these discrepancies between the model and the empirical data, a follow-on effort will be performed in an attempt to better capture the formation of the large expansion plume seen in the high-speed video. Specifically, phase changes in the liquid and gas will be addressed in the follow-on effort, as will turbulence effects on mixing at small scales.