Abstract
A novel hybrid multiphase flow solver has been used to conduct simulations of a vertical plunging liquid jet. This solver combines a multifluid methodology with selective interface sharpening to enable simulation of both the initial jet impingement and the long-time entrained bubble plume phenomena. Models are implemented for variable bubble size capturing and dynamic switching of interface sharpened regions to capture transitions between the initially fully segregated flow types into the dispersed bubbly flow regime. It was found that the solver was able to capture the salient features of the flow phenomena under study and areas for quantitative improvement have been explored and identified. In particular, a population balance approach is employed and detailed calibration of the underlying models with experimental data is required to enable quantitative prediction of bubble size and distribution to capture the transition between segregated and dispersed flow types with greater fidelity.
Highlights
While computational fluid dynamics (CFD) methods have advanced in many areas such that predictive modeling is possible, multiphase flows remain an area where prediction is yet out of reach for the majority of applications
Simulations using the standard solver were conducted for two different values of the dispersed phase bubble size: 2 mm and 500 micron each for both sharpened (Cα = 1) and unsharpened (Cα = 0) settings giving a total of four configurations
When deactivation of interface sharpening was more substantial and predicted bubble size for the dispersed phase remained small, the simulation tended toward multifluid physics with a large dispersed plume and low entrainment
Summary
While computational fluid dynamics (CFD) methods have advanced in many areas such that predictive modeling is possible (e.g., external aerodynamics), multiphase flows remain an area where prediction is yet out of reach for the majority of applications. Free surface flows in which the dynamics of a fluid-fluid interface is important to the overall physics under investigation are typically modeled with a shared momentum equation and a phase fraction field using a sharp interface capturing method such as Volume of Fluid and level set or the like where fluid interfaces are resolved on or by, in the case of interface tracking methods, the computational mesh Such methods are infeasible for simulation of dispersed flows characterized by many small fluid particles (bubbles/droplets) which cannot be fully resolved on a computation mesh. In such cases, a so-called multifluid or Euler-Euler approach is taken in which phases are treated as interpenetrating continua, each governed by its own momentum equation and having exchange terms to account for interphase momentum transfer (drag, lift, virtual mass, etc.). A hybrid CFD solver has been developed which aims to overcome the issue of regime dependency by combining the Euler-Euler multifluid method with sharp interface capturing in a regime flexible framework [1]
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