Analysis of vertical co-current air-water flow with the Neptune_CFD

A two-fluid modelling approach with interface sharpening is applied for numerical simulations of flooding waves in air-water co-current flow in vertical pipe. The simulation capability of Neptune_CFD code is analysed. The results are compared with experimental data and with the simulations performed with the computational code ANSYS CFX. Isothermal flow of air and water in the churn flow regime is modelled. Turbulence is modelled for each phase separately using URANS approach. A typical geometry of a test section in the vicinity of the liquid injector is used as the computational domain. In general, both computational codes predicted similar wave frequency values for the pipe with internal diameter of 32 mm and show good agreement with the experimental data. Detailed analysis of local flow phenomena in the case of 2D Neptune_CFD simulation however reveals a significant accumulation of liquid in the centre of the pipe that may be attributed to the axisymmetric assumption, drag force formulation, and possible numerical errors. It was demonstrated that the liquid accumulation in the centre of the pipe can be avoided by the simulations in the full 3D domain due to asymmetric nature of the churn flow.