Development and Application of Interfacial Anti-Diffusion and Poor Mesh Numerics Treatments for Free Surface Flows.

Volume of Fluid (VOF) method is widely used to simulate free surface flows. There are various interface tracking and capturing schemes available with this model. The explicit interface tracking scheme based on geometrical reconstruction of the interface is the most accurate but computationally expensive. On the other hand, there are interface capturing schemes based on algebraic formulation that are comparatively more diffusive but computationally less expensive. These interface capturing schemes can be used with implicit and explicit volume fraction formulations. For industrial strength cases, the use of implicit schemes is increasing as it is a good compromise between speed and accuracy. In meshing such complex geometries, there is a tradeoff between the cell count and the quality of mesh. While resolving the key areas with good quality mesh and keeping the cell count within acceptable limit, sometimes quality of mesh in certain regions suffers. Such regions may contain highly skewed cells, cells with high aspect ratio or high cell-jumps. Such mesh can have issues in convergence, worsen the issue of interfacial diffusion and lead to inaccurate results. In the present work, two numerical treatments called interfacial anti-diffusion and poor mesh numerics are developed and implemented in ANSYS Fluent R16. Interfacial anti-diffusion treatment helps reduce the numerical diffusion and sharpen the interface. Poor mesh numerics treatment identifies cells with bad quality and applies appropriate numerical treatment to help stability and convergence. Results of test cases and an industrial strength case are reported with and without these treatments. It is shown that using these treatment results in improvement of stability and accuracy. For the industrial strength case, the results are in good agreement with the experimental data.