Modeling convection

To model convection, you can:

• Use the options on the 3D Flow page of the Solution dialog box for coupled thermal-flow analyses.

• Use the Convection to Environment constraint command.

You can use either approach, or combine the two by defining 3D flow convection on one section of the model, and Convection to Environment constraints on another section.

Using the 3D Flow options in Coupled Thermal-Flow analyses

The options on the 3D Flow page of the Solution dialog box let you explicitly model the movement of all 3D fluid elements in the model in coupled thermal-flow analyses. In those analyses, the flow solver uses Computational Fluid Dynamics (CFD) equations to solve the flow model. The software solves the thermal model separately and couples it to the flow model by convection where the fluid elements contact the thermal elements. Only a coupled solution can include 3D flow convection.

You can specify 3D flow convection for a coupled thermal-flow analysis in three ways:

• You can define convection parameters for the whole model on the 3D Flow page of the Solution dialog box.

• You can mesh the convecting surfaces and bodies with thermal elements and define the surfaces in a Flow Surface simulation object and the bodies in a Flow Blockage simulation object. See Flow Surface and Flow Blockage.

• You can use a combination of the first two methods. First use the options on the 3D Flow page of the Solution dialog box to define convection with parameters appropriate to most surfaces in your model. Then, create a Flow Surface simulation object on any faces where the convection differs from the default. A Flow Surface or Flow Blockage simulation object included in the solution always overrides default convection parameters for the selected geometry.

By default, the flow solver models convection with these properties on every surface in contact with the fluid, with the following exceptions:

• A face that divides fluid elements on one side from fluid elements on the other. The fluid passes through such a surface; thus it cannot convect.

• The face is defined as a Flow Surface or Flow Blockage simulation object with its own convection properties and roughness defined.

You can deactivate default convection by clearing the Non-fluid 2D and 3D Elements Block Flow check box on the 3D Flow page of the Solution dialog box. With this option cleared, you must define a surface as a Flow Surface simulation object or a solid as a Flow Blockage simulation object for it to convect.

Using the Convection to Environment constraint

The Convection to Environment constraint simulates convection for one or more surfaces by implicitly modeling the movement of fluid at a specific temperature in contact with the surfaces. You can define a convection coefficient, or submit information that allows the thermal solver to calculate a convection coefficient for the surfaces.

Either thermal solutions or coupled solutions can include Convection to Environment constraints. With a Convection to Environment constraint, the thermal solver uses the specified fluid temperature and the specified or calculated convection coefficient to simulate heat exchange between the fluid and the selected surfaces.

See Convection to Environment for more information.

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Modeling convection, Simcenter 3D 2021.1 Series

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