Specify how the reference length scale is defined:

•The default setting is Automatic, in which case the wall distance is automatically evaluated as:

where d is the dimension of the geometry (for example, 3 for a 3D geometry). If the geometry is very slender, Equation 8-1 tends to give a result that is too large. Then define lref manually.

•Select User defined to define a value or expression for the wall distance Reference length (SI unit: m) in the associated field.

M O D E L I N P U T S

Specify the temperature to be used in the interface:

•Select User defined to enter a value or expression for the temperature (SI unit: K) in the corresponding field. This input is always available.

•In addition, select a temperature defined by a heat transfer interface present in the model (if any). For example, then select Temperature (ht/fluid1) to use the temperature defined by the feature fluid1 in the heat transfer interface ht.

To define the Absolute Pressure, see the settings for the Heat Transfer in

Fluids node as described in the COMSOL Multiphysics User’s Guide.

Tip

Initial Values

The Initial Values node adds an initial value for the flow variables and the effective gas density that can serve as an initial condition for a transient simulation or as an initial guess for a nonlinear solver.

D O M A I N S E L E C T I O N

From the Selection list, choose the domains to define the initial values.

I N I T I A L V A L U E S

Enter values or expressions for the initial value of the velocity field u in the Velocity field fields (SI unit: m/s) and for the pressure p in the Pressure field (SI unit: Pa). The

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default values are 0. Also enter a value or expression for the initial value of the Effective gas density in the corresponding field (SI unit: kg/m3).

If Solve for interfacial area is activated; enter an initial value for the Number density nd

(SI unit: 1/m3) in the corresponding field.

In a turbulent flow interface, initial values for the turbulence variables are also specified. By default these are specified using the predefined variables defined by the expressions in Initial Values.

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