The Bubbly Flow, Realizable k-ε Interface
The Bubbly Flow, Realizable k-ε(bf) interface (), found under the Multiphase Flow>Bubbly Flow>Bubbly Flow, Turbulent Flow branch () when adding a physics interface, is used to model the flow of liquids with dispersed bubbles at high Reynolds numbers.
It is assumed that the bubbles only occupy a small volume fraction and that they always travel with their terminal velocity. It is thereby possible to solve only one set of Navier–Stokes equations for the liquid phase and to let the velocity of the bubbles be guided by a slip model. The pressure distribution is calculated from a mixture-averaged continuity equation. The volume fraction of bubbles is tracked by solving a transport equation for the effective gas density. Turbulence effects are modeled using the realizable two-equation k-ε model and bubble-induced turbulence production. The flow near walls is modeled using wall functions.
The physics interface can also model the distribution of the number density, which can be used to calculate the interfacial area, useful when simulating chemical reactions in the mixture.
The main physics node is the Fluid Properties feature, which adds the equations for turbulent bubbly flow and provides an interface for defining the fluid materials for the liquid and the gas and the slip velocity model to use.
When this physics interface is added, the following default physics nodes are also added in the Model Builder — Fluid Properties, Wall (the default boundary types are No slip for the liquid and No gas flux for the gas), and Initial Values.
Except where indicated below, the nodes settings for this physics interface are the same as for The Laminar Bubbly Flow Interface and The Bubbly Flow, k-ε Interface.
Turbulence
The default Turbulence model type is RANS. A different turbulence model can be selected under Turbulence model. The default turbulence model is Realizable k-ε.
Wall Treatment
Wall treatment for the Realizable k-ε model can only be set to Wall functions. More options becomes available by selecting another option under Turbulence model.
Edit Turbulence Model Parameters
Turbulence model parameters are optimized to fit as many flow types as possible, but for some special cases, better performance can be obtained by tuning the model parameters. For a description of the turbulence model and the included model parameters see Theory for the Turbulent Flow Interfaces.
Dependent Variables
The dependent variables (field variables) are the Velocity field, liquid phase u (SI unit: m/s), the Pressure p (SI unit: Pa), the Effective gas density rhogeff (SI unit: kg/m3), the Turbulent dissipation rate ep (SI unit: m2/s3), the Turbulent kinetic energy k (SI unit: m2/s2), and the Number density, gas phase nd (SI unit: 1/m3).