Direct Numerical Simulation of Condensing Stratified Flow

The paper discusses the results of a detailed direct numerical simulation study of condensing stratified flow, involving a sheared steam-water interface under various thermal and turbulent conditions. The flow system comprises a superheated steam and subcooled water flowing in opposite directions. The transport equations for the two fluids are alternately solved in separate domains and then coupled at the interface by imposing mass, momentum, and energy jump conditions with phase change. The effects induced by changes in the interfacial shear were analyzed by comparing the relevant statistical flow properties. New scaling laws for the normalized heat transfer coefficient (HTC), K+, have been derived for both the steam and liquid phases. The steam-side law is found to compare with the passive-scalar law obtained hitherto by (Lakehal et al.(2003, “Direct Numerical Simulation of Turbulent Heat Transfer Across a Mobile, Sheared Gas-Liquid Interfaces,” ASME J. Heat Transfer, 125, pp. 1129–1139) in that HTC scales with Pr−3∕5. A close inspection of the transfer rates on the liquid side reveals a consistent relationship between K+, the local wave deformation or curvature and the interfacial shear stress. The surface divergence model of Banerjee et al. (2004, “Surface Divergence Models for Scalar Exchange Between Turbulent Streams,” Int. J. Multiphase Flow, 30(8), pp. 965–977) is found to apply in the liquid phase, too.