Morphology‐adaptive multiphase models are becoming more established for the numerical description of complex gas‐liquid flows adapting dynamically to the local flow morphology. In the present study, two different numerical methods originally designed for distinct flow morphologies are combined, namely the volume‐of‐fluid and the Euler–Euler method. Both edge cases have been proven to be capable of delivering reliable predictions in the respective use cases. The long‐term goal is to improve the prediction of gas‐liquid flows, regardless of the flow regime in a specific application. To capture the system dynamics with a given grid resolution, the flow fields need to be predicted as precise as possible, while the shape of structures such as gas bubbles need to be recovered adequately in topology and shape. The goal is to obtain reliable predictions on intermediate mesh resolutions rather than relying on fine meshes requiring more computational resources. Therefore, a procedure is proposed to locally measure the degree of resolution. With this information, the hydrodynamics in the interface region can be controlled by means of a dedicated interfacial drag formulation in order to improve simulation results across several levels of spatial resolution. A modified formulation of buoyancy is proposed to prevent unphysical oscillations of vertical velocity near a horizontal interface. The functionality is demonstrated in a three‐dimensional case of a gas bubble rising in stagnant liquid and in a co‐current stratified air‐water channel flow in two‐dimensional space. The choice of these different applications demonstrates the general applicability of the proposed model framework.
A transient simulation of air-water counter-current flow by the means of two-fluid model with interface sharpening is performed. The gas-liquid inhomogeneous model with both phases considered as incompressible is used. Turbulence is modelled for each phase separately using the two-equation eddy viscosity model. The numerical domain consists of an axisymmetric wedge with the porous wall inlet region representing a vertical pipe experimental test section. Evolution of volume fraction, velocities and pressure variations along the interface is presented. Simulation results are compared with the known experimental data (from the literature) for the wave frequency and velocity. The present simulation is also compared to a known numerical simulation found in literature that used volume of fluid method. Sensitivity study of several modelling parameters is performed to evaluate and discuss their impact on simulation results in an attempt to establish best practice guidelines for modelling of realistic counter-current flows, important in nuclear reactor systems.
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