Numerical Simulation of Turbulent Mist Flows With Liquid Film Formation in Curved Pipes Using an Eulerian–Eulerian Method

Abstract

Turbulent flows of air/water mixtures through curved pipes are modeled in this work using a Eulerian–Eulerian method. This is motivated by the possibility of using computational fluid dynamics (CFD) as a design tool applied to curved pipes feeding a gas/liquid separator. The question is to identify the curvature of such pipes that can promote film formation upstream of the separator and, thus, precondition the flow without creating a large pressure drop. The performance of the mixture theory with a drift flux model and the “realizable” k-ε closure was evaluated in the simulations. The enhanced wall treatment (EWT) was utilized to resolve the flow in the near-wall region. A qualitative study was first conducted to investigate the flow patterns and the liquid film formation in a 180 deg bend. The numerical results were validated by comparing the computed pressure drop with empirical correlations from the literature. Subsequently, the importance of droplet size and liquid volume fraction was investigated by studying their effect on the flow patterns of the continuous phase, as well as their impact on the secondary flow intensity, the pressure drop, and the liquid film formation on the wall. Various pipe geometries were studied to achieve a low pressure drop while maintaining a high droplet deposition. Results show that a combination of the drift flux model with the realizable k-ε closure and EWT for the near-wall treatment appears capable of capturing the complex secondary flow patterns such as those associated with film inversion. The pressure drop computed for various flows appear to be in good agreement with an empirical correlation. Finally, bends with a curvature ratio around 7 appear to be the optimal for providing a small pressure drop as well as a high droplet deposition efficiency in a U-bend.