Effect of interfacial drag force on the numerical stability of the two-step method in the two-fluid model

The stability limit of the implicit Courant-Eulerian (ICE) method was enhanced by adding a stabilization step to the basic ICE method such as the stability enhancing two-step (SETS) method implemented in TRAC-PF1. The matrix size of the SETS method is smaller than that of the fully implicit methods. However, the momentum stabilization steps enlarge the matrix size of the SETS method as the dimension increases. In order to reduce the matrix size of the SETS method in multidimensional problems and to study the effect of the interfacial drag force on stability, a von Neumann stability analysis of the SETS method without momentum stabilization steps (SETS-WM) is presented here. It is found that the interfacial drag force extends the stability limit considerably. When SETS-WM is tested numerically, stability problems have not been encounted when the time step is restricted by the stability limit derived here. (orig.)