Two-phase modeling of water-air flow of dispersed and segregated flows

Abstract

The accuracy of the Eulerian two-fluid model to solve dispersed and segregated multiphase flows was evaluated. Five air-water tests representing flow regimes commonly found in nuclear installations were considered: (a) bubbles ascending in a stagnation water column, (b) air-water upward flow crossing an obstacle in a vertical column, (c) liquid-liquid co-current horizontal flow, (d) air-water counter-current horizontal flow, and (e) air injection and swelling in the vertical water colu mn. The first four tests corresponded to steady-state benchmarks reported in the literature, and the last one was an experimental test proposed to assess the computational model under transient high void fraction flow. The five cases were simulated using the same set of interfacial force models in order to find one computational model suitable to solve all the regimes thanks to the use of a linear blending method to automatically switch the interfacial models accounting for the local rheology of the flow (drops in air, bubbles in water, segregated flow). The dispersed flow cases (cases a, b and e) were suitably modeled using the models proposed by Grace (drag), Tomiyama (lift), Frank (wall lubrication), and Burn (turbulent dispersion). On the other hand, the segregated systems (cases c and d) were solved using the drag model proposed by Marschall. Regarding turbulence, the κ-ω SST model was appropriated for both cases.