Numerical simulation of mixing zone growth between two fluids under acceleration

Numerical simulations are performed on the propulsion of a liquid slug which is driven through a tube by a gas at high pressure (10 MPa). A 2D axisymmetric CFD model is used to study the evolution of a turbulent mixing zone between the slug and the air, which forms due to Rayleigh-Taylor instability (RTI) caused by the relative difference in density between the slug and the driver gas. The dependency of the mixing zone growth rate on several parameters such as fluid type (density, viscosity), and pipe diameter is analyzed by performing several parametric simulations. Over the range of fluids simulated in the model, the Atwood number varies from 0.75 to 0.80 while the Reynolds number varies from approximately 103 to 106. The model shows that the mixing zone growth rate is sensitive to both the type of fluid and the aspect ratio of the fluid slug.