A Hybrid Dispersed-Large Interface Solver for multi-scale two-phase flow modelling

Abstract

Hybrid multiphase flows are flows with both dispersed phase and large scale structures, and generally have a wide range of interfacial length scales. Such flows are common in industrial flow problems and nuclear engineering applications. Appropriate modelling of these scales, ranging from the dispersed to the segregated flow regime, becomes important as they all contribute to the overall behaviour of the flow physics. Conventional two-fluid, two-field Eulerian-Eulerian solvers have been known to neglect important aspects of flow physics and are unable to reproduce such hybrid flows. A systematic benchmark of a hybrid solver named Hybrid Dispresed-Large Interface Solver (HD-LIS) is presented here. A flow regime map based on the gas volume fraction is utilised in the present solver in order to distinguish between dispersed and segregated flow regimes and for application of the appropriate physical models and numerical schemes in each regime. The modelling of segregated regime includes an appropriate drag force, interface compression scheme, and turbulence damping, while modelling of the dispersed regime considers both drag and non-drag momentum exchange forces. In addition, the use of total variation diminishing (TVD) numerical schemes and semi-implicit temporal discretization approach ensures boundedness and robustness of the solver. The present benchmark includes a wide spectrum of test cases, selected to test the ability of the solver in fundamental modelling of dispersed phase or large scale interfaces These validation cases include single bubble and droplet dynamics, flow regimes transition (between dispersed and plug flows), free-surface impact jet, and two-phase shear flows. It is shown that the present solver is able to qualitatively reproduce both dispersed and segregated flow physics well. As will be demonstrated, HD-LIS differs from other existing Eulerian-Eulerian two-fluid solvers which are reported in literature in respect to the applied numerical schemes and physical models. This selection of schemes and models is shown to make the solver suitable for modelling of underlying flow physics exhibited by dispersed flows and large-scale interfaces. Although the validation cases presented herein offer limited flow complexity, the present solver is considered a step towards a more comprehensive hybrid solver.