T h e N o n - I s o t h e r m a l F l o w a n d

C o n j u g a t e H e a t T r a n s f e r , L a m i n a r F l o w I n t e r f a c e s

As discussed and as per Table 12-1, these two interfaces differ only by where they are selected in the Model Wizard and the default model selected—Heat transfer in solids or Fluids. Most of the other features share the same setting options as described in this section and in Shared Interface Features.

In this section:

•The Non-Isothermal Flow, Laminar Flow Interface

•The Conjugate Heat Transfer, Laminar Flow Interface

The Non-Isothermal Flow, Laminar Flow Interface

The Non-Isothermal Flow version of the Laminar Flow interface (), found under the

Fluid Flow>Non-Isothermal Flow branch () of the Model Wizard, is a predefined multiphysics coupling consisting of a single-phase flow interface, using a compressible formulation, in combination with a Heat Transfer interface. When this interface is added, these nodes are added by default—Non-Isothermal Flow, Fluid, Wall, Thermal Insulation, and Initial Values.

Right-click any node to add other features that implement, for example, boundary conditions, volume forces, or heat sources.

•Fluid Damper: Model Library path CFD_Module>Non-Isothermal

Flow>fluid_damper

Model

This interface changes to a Conjugate Heat Transfer interface when Heat

transfer in solids is selected as the Default model.

Tip

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I N T E R F A C E I D E N T I F I E R

The interface identifier is a text string that can be used to reference the respective physics interface if appropriate. Such situations could occur when coupling this interface to another physics interface, or when trying to identify and use variables defined by this physics interface, which is used to reach the fields and variables in expressions, for example. It can be changed to any unique string in the Identifier field.

The default identifier (for the first interface in the model) is nitf.

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

The default setting is to include All domains in the model to define the dependent variables and the equations. To choose specific domains, select Manual from the

Selection list.

P H Y S I C A L M O D E L

Define interface properties to control the overall type of model:

Neglect Inertial Term (Stokes Flow)—All Interfaces

Select the Neglect inertial term (Stokes flow) check box to model flow at very low Reynolds numbers where the inertial term in the Navier-Stokes equations can be neglected. Instead use the linear Stokes equations. This flow type is referred to as creeping flow or Stokes flow and can occur in microfluidics (and MEMS devices), where the flow length scales are very small.

Turbulence Model Type

By definition, no turbulence model is needed when studying laminar flows. The default Turbulence model type is None.

The flow state in a fluid-flow model is not, however, always known beforehand. Select

RANS as the Turbulence model type and select any of k- , k- , Low Re number k- or

Spalart-Allmaras as Turbulence model in order to account for turbulence. This changes the interface into the turbulent version. See the Turbulent Flow Interfaces for details.

If the default Turbulence model type selected is RANS, the additional turbulence model settings are made available. However, the node is still

called Non-Isothermal Flow or Conjugate Heat Transfer with a number

Note

added at the end of the name to indicate the change.

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Default Model

For the Non-Isothermal Flow interface the Default model is Fluid. For the Conjugate Heat Transfer interface the Default model is Heat transfer in solids.

Shallow Channel Approximation

When activated the Shallow channel approximation and out-of-plane heat transfer check box simultaneously activates the shallow channel

approximation for the Navier-Stokes equations and the out-of-plane

2D features for the heat transfer. When selected, enter the domain Thickness dz (SI unit: m).

D E P E N D E N T V A R I A B L E S

The dependent variables (field variables) are for the Velocity field, Pressure, and Temperature. The names can be changed but the names of fields and dependent variables must be unique within a model.

For turbulence modeling and heat radiation, there are additional dependent variables for the turbulent dissipation rate, turbulent kinetic energy, reciprocal wall distance, and surface radiosity.

D I S C R E T I Z A T I O N

To display this section, click the Show button () and select Discretization. Select a

Discretization of fluids—P1+P1 (the default), P2+P1, or P3+P2. The first term describes the element order for the velocity components, and the second term is the order for the pressure. The element order for the temperature is set to follow the velocity order, so the temperature order is 1 for P1+P1, 2 for P2+P1, and 3 for P3+P2.

C O N S I S T E N T A N D I N C O N S I S T E N T S T A B I L I Z A T I O N

To display this section, click the Show button () and select Stabilization. The consistent stabilization methods are applicable to the Heat and flow equations. The

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