Improvements in Free Surface Flow Numerics Using Coupled VOF and Pseudo Transient Solver

This paper presents numerical methodologies for the robust, accurate and faster solution of the steady state free surface flows. Numerical solution of free surface flow problems using pressure based coupled solver is emerging trend in CFD community that allows implicit coupling of pressure, velocity and volume fractions and provides quiet robust and faster solution. Due to strong presence of body forces in free surface flow applications, implicit treatment of body forces is also a critical aspect for faster reduction of modulations in converged quantities. Free surface problems in steady state often suffer from poor diagonal dominance in system of equations, which could be improved by the usage of pseudo-transient solver, which not only improves the diagonal dominance but also inherently facilitates the local under-relaxation of solution variables. Pressure based coupled algorithm in conjunction with pseudo-transient solver overcomes most of the difficulties associated with robustness, stability and speed-up of free surface steady state simulations. Various case studies related to steady state open channel flow are considered in this paper, which clearly demonstrate the superiority of solving the volume fraction equation in coupled manner compared to solving it in a segregated manner. Convergence behavior of solution variables along with drag monitors are emphasized in the analysis and results have been compared with analytical or experimental data, which are in good agreement.