Influence of near-wall modelling on boiling flow simulation

The capability of the three-dimensional two-fluid codes to simulate the local boiling flow processes has been assessed. Boiling flow experiments of Roy et al. [Roy, R.P., Kang, S., Zarate, J.A., Laporta, A., 2002. Turbulent subcooled boiling flow—experiments and simulations, J. Heat Transfer 124, 73–93] and Lee et al. [Lee, T.H., Park, G.C., Lee, D.J., 2002. Local flow characteristics of subcooled boiling flow of water in a vertical concentric annulus. Int. J. Multiphase Flow 28, 1351–1368], both performed in annular vertical channels were used as an experimental benchmark data set. The boiling flow is strongly affected by local mechanisms in the boundary layer near the heated wall. In this paper, the influence of near-wall modelling on the distribution of flow parameters at flow boiling has been analyzed. A generic wall function model for 3D two-fluid codes, based on surface roughness analogy has been proposed instead of commonly used single-phase log-law model. The new model has been implemented in the code CFX-4.4. In general, better agreement of phase velocities with experimental data were obtained with the new model. Presented results show that the influence of nucleating bubbles on the near-wall velocity profile should be taken into account. The second goal of this paper is to compare the NEPTUNE_CFD simulations against CFX-4.4 results and experimental data.