Three-dimensional simulations of liquid waves in isothermal vertical churn flow with OpenFOAM

Periodic liquid waves of large amplitude are one of characteristic phenomena observed in the churn flow regime of gas-liquid flow in vertical conduits, where the liquid flowing on the wall is entrained upwards by the gas flow in the core. The present work investigates the frequency of these large liquid waves. Three-dimensional simulations of isothermal churn flow of air and water in 19 and 32 mm vertical pipes were performed using the interFoam solver from the OpenFOAM library. Turbulent features in the flow are modelled using the unsteady Reynolds Averaged Navier-Stokes approach with the k-omega SST (shear stress transport) model. Interface sharpening with bounded compression was used to preserve the sharpness of gas-liquid interface by compensating the diffusive fluxes of the numerical scheme. A sensitivity study on the global amount of interface compression was performed for two flow cases taken from the literature. Mesh sensitivity study was performed using four meshes, ranging from a coarse mesh with several hundred thousand cells, to a fine mesh with several million computational cells. Results for the calculated wave frequency and wave maximum amplitude agree with measured values reported in the literature.