When the effects of thermal and solutal buoyancy are present, a flow can be induced inside the domain due to the effect of gravity on the variable density of the medium. In the case of multi-component solidification problems, the density variation takes place due to temperature changes and also due to species concentration gradients near the liquid-solid interface. The flow due to buoyancy with solidification and melting can be modeled in Ansys Fluent using the thermal and solutal buoyancy options.
For more information on the theory behind buoyancy induced flow in solidification and melting problems, see Thermal and Solutal Buoyancy in the Theory Guide.
The procedure for setting up a solidification/melting problem is described in Setup Procedure. To include thermal and solutal buoyancy effects, perform the following steps:
Enable the Include Thermal Buoyancy and Include Solutal Buoyancy options in the Solidification and Melting dialog box (Figure 27.3: The Solidification and Melting Dialog Box).
Note: The Include Thermal Buoyancy and Include Solutal Buoyancy options are available only when solidification is modeled with species transport.
Define the operating conditions and properties for modeling thermal buoyancy as described in Buoyancy-Driven Flows and Natural Convection.
To model solutal buoyancy, specify a value for the Solutal Expansion Coefficient for all the species except the last one in the mixture in the Create/Edit Materials dialog box.
Note: By default, the eutectic mass fraction of the solute is used as the reference species mass fraction of the solute for the calculation of the body force due to solutal buoyancy. Therefore, no additional input is required. However, in certain applications, it is not always desirable to use the default values of the reference mass fraction. For such cases, the solute mass fraction values can be entered through text user interface as follows:
define/models/solidification-melting? yes Include Thermal Buoyancy? yes Include Solutal Buoyancy? yes Use reference mass fraction of solutes? yes Reference mass fraction of the species-i "value"