A stabilized two-fluid non-equilibrium method for collocated grids using momentum interpolation and flux reconstruction

Collocated grids can induce pressure–velocity decoupling due to non-compact discretization stencils. The interpretation of non-equilibrium two-phase dynamics on collocated grids depends critically on how the modeled momentum is transferred between cell centers and conservative face fluxes. This study proposes a methodology for the two-fluid non-equilibrium model based on center-to-face momentum interpolation and face-to-center full-flux reconstruction. The pseudo-momentum formulation relates the complete modeled momentum balance between cell centers and conservative face fluxes and thereby reduces checkerboard pressure modes and spurious cell-centered velocity oscillations. The benchmark sequence relates the mechanism to conservative phase-boundary transport, transient inertia-gravity exchange, gravity-driven front propagation, mechanical non-equilibrium, and boiling phenomena. The results indicate that the proposed complete formulation improves the consistency of the pressure field, phasic velocities, void fraction, and interfacial momentum response in resolved non-equilibrium dynamics, while the boiling and drag behaviors remain governed by the underlying constitutive models. This work provides a stable, accurate, and extensible approach for simulating two-phase flows with non-equilibrium and phase change.