Direct Numerical Simulation of Multiphase Flow
A wide range of natural phenomena and engineering processes related to multiphase flow in nuclear reactors and heat exchangers, as well as the carbon dioxide sequestration processes in saline aquifers and oil reservoirs, deal with the flow of multiple fluid phases involving heat, mass and momentum transport across phase boundaries. Multiphase aspects in such applications range from the isothermal flow of bubbles and droplets to more complex flows undergoing evaporation, condensation and solidification. The success of a numerical simulation to accurately characterize multiphase behavior across multiple scales depends on its ability to properly incorporate phase interaction constructs associated with interfaces and contact lines at both the fluid-continuum and molecular scales.
We have developed new numerical techniques to solve the Navier-Stokes equations for multiple fluids that allow the numerical solution to conserve mass across phase interfaces without degrading the accuracy of the interface geometry while also maintaining the correct momentum transport for variable density fluids. Traditional numerical methods introduce momentum transport errors by ignoring the time rate of change of density in the solution of the global pressure. They are also limited to preserving the accuracy of either the phase mass with the Volume of Fluid Method or the interface geometry with the level-set reinitialization method. In contrast our numerical method accurately handles all three fundamental issues through the use of phase based pressure solution and special techniques of interpolating the level-set function across the interface without reinitialization. This allows us to investigate practical processes involving phase change in a rigorous manner for the first time based on the physically correct underlying fluid dynamic solution. This capability does not exist currently within NETL-RUA.
The Figure presents the result of a typical numerical simulation of multiphase flow based on full Navier-Stokes equations obtained with our method. The figure shows the interface configuration in a hypothetical porous matrix (filled circles indicate solids) where CO2 (blue) is displacing brine from the left. Streamlines (black lines with arrows) indicate the velocity field. This effort directly addresses the objectives of developing physics-based simulations to achieve highly efficient, environmentally acceptable energy technologies and processes.