LES of turbulent non-isothermal two-phase flows within a multifield approach

Abstract

Safety issues in nuclear power plant involve complex turbulent bubbly flows. To predict the behavior of these flows, the two-fluid approach is often used. Nevertheless, this model has been developed for the simulation of small spherical bubbles, considered as a dispersed field. To deal with bubbles with a large range of sizes, a multifield approach based on this two-fluid model has been proposed. A special treatment, called the Large Bubble Model (LBMo), has been implemented and coupled to the dispersed model. However, only laminar and isothermal flows were considered in previous papers. Thus, here, Large Eddy Simulations (LES) are investigated to model turbulence effects. For this purpose, the two-fluid model equations are filtered to highlight the specific subgrid terms. Then, an a priori LES study using filtered Direct Numerical Simulation (DNS) results is detailed. This analysis allows classifying these terms according to their relative weight and then concentrating the modelling efforts on the predominant ones. Five different turbulence models are compared. These results are finally used to perform true LES on a turbulent two-phase flow. Moreover, in order to tackle non-isothermal flows occurring in industrial studies, a new heat transfer model is implemented and validated to deal with phase change at large interfaces using the Large Bubble Model.