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# 28.2 Fluid continuum elements

• “Fluid (continuum) elements,” Section 28.2.1   
• “Fluid element library,” Section 28.2.2

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# 28.2.1 FLUID (CONTINUUM) ELEMENTS

Products: Abaqus/CFD Abaqus/CAE

# References

• “Fluid element library,” Section 28.2.2   
• “Creating homogeneous fluid sections,” Section 12.13.13 of the Abaqus/CAE User’s Guide, in the HTML version of this guide

# Overview

Fluid elements are provided to discretize the domain in Abaqus/CFD. These elements can be referenced by a fluid section to define a fluid domain or by a solid section to define a solid domain in an Abaqus/CFD solid heat transfer analysis.

# Choosing an appropriate element

Three-dimensional fluid elements are available.

# Naming convention

Fluid elements in Abaqus are named as follows:

![](images/page-203_8797671efb997d4f1ccd4ba8b06b7c4371701abb553ee89de78fb2c586407a34.jpg)

<details>
<summary>text_image</summary>

FC 3D 4
number of nodes
three-dimensional
fluid continuum
</details>

For example, FC3D8 is a three-dimensional, 8-node brick fluid element.

# Active fields for fluid elements

The fields active in a fluid flow analysis are not determined by the element type but by the analysis procedure and its options. The sole purpose of the element type is to define the shape of the element used to discretize the continuum.

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# 28.2.2 FLUID ELEMENT LIBRARY

Products: Abaqus/CFD Abaqus/CAE

# Reference

• “Fluid (continuum) elements,” Section 28.2.1

# Overview

This section provides a reference to the fluid elements available in Abaqus/CFD.

# Element types

Fluid elements 

<table><tr><td>FC3D4</td><td>4-node tetrahedron</td></tr><tr><td>FC3D5</td><td>5-node pyramid</td></tr><tr><td>FC3D6</td><td>6-node prism</td></tr><tr><td>FC3D8</td><td>8-node brick</td></tr></table>

Active degrees of freedom

The active degrees of freedom depend on the analysis procedure and options, such as the energy equation and turbulence model. For more information, see “Active degrees of freedom” in “Boundary conditions in Abaqus/CFD,” Section 34.3.2.

Additional solution variables

None.

# Nodal coordinates required

X, Y, Z

# Element property definition

<table><tr><td>Input File Usage:</td><td>Use the following option to define the element properties for flows:*FLUID SECTIONUse the following option to define the element properties for heat transfer without flows:*SOLID SECTION</td></tr><tr><td>Abaqus/CAE Usage:</td><td>In Abaqus/CAE you can only define the element properties for flows.Property module:Create Section:select Fluid as the section</td></tr></table>

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# Distributed loads

Distributed loads are available for all fluid element types. They are specified as described in “Distributed loads,” Section 34.4.3.

<table><tr><td>Load ID (*DLOAD)</td><td>Abaqus/CAE Load/Interaction</td><td>Units</td><td>Description</td></tr><tr><td>BX</td><td>Body force</td><td> $FL^{-3}$ </td><td>Body force in global X-direction.</td></tr><tr><td>BY</td><td>Body force</td><td> $FL^{-3}$ </td><td>Body force in global Y-direction.</td></tr><tr><td>BZ</td><td>Body force</td><td> $FL^{-3}$ </td><td>Body force in global Z-direction.</td></tr><tr><td>GRAV</td><td>Gravity</td><td> $LT^{-2}$ </td><td>Gravity loading in a specified direction (magnitude is input as acceleration).</td></tr><tr><td>PDBF</td><td>Porous drag body force</td><td>None</td><td>Porous drag body force load (specify porosity as the input).</td></tr></table>

# Distributed heat fluxes

Distributed heat fluxes are available when the temperature equation is activated on the analysis procedure. They are specified as described in “Thermal loads,” Section 34.4.4.

<table><tr><td>Load ID(*DFLUX)</td><td>Abaqus/CAELoad/Interaction</td><td>Units</td><td>Description</td></tr><tr><td>BF</td><td>Body heat flux</td><td> $JL^{-3}T^{-1}$ </td><td>Heat body flux per unit volume.</td></tr></table>

# Surface-based loading

# Distributed heat fluxes

Surface-based heat fluxes are available for all elements when the temperature equation is activated on the analysis procedure. They are specified as described in “Thermal loads,” Section 34.4.4.

<table><tr><td>Load ID(*DSFLUX)</td><td>Abaqus/CAELoad/Interaction</td><td>Units</td><td>Description</td></tr><tr><td>S</td><td>Surface heat flux</td><td> $JL^{-2}T^{-1}$ </td><td>Heat surface flux per unit area into the element surface.</td></tr></table>

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# Film conditions

Surface-based film conditions are available for all elements when the temperature equation is activated on the analysis procedure. They are specified as described in “Thermal loads,” Section 34.4.4.

<table><tr><td>Load ID(*SFILM)</td><td>Abaqus/CAELoad/Interaction</td><td>Units</td><td>Description</td></tr><tr><td>F</td><td>Surface film condition</td><td> $JL^{-2}T^{-1}\theta^{-1}$ </td><td>Film coefficient and sink temperature (units of  $\theta$ ) provided on the element surface.</td></tr></table>

# Radiation types

Surface-based radiation conditions are available for all elements when the temperature equation is activated on the analysis procedure. They are specified as described in “Thermal loads,” Section 34.4.4.

<table><tr><td>Load ID(*SRADIATE)</td><td>Abaqus/CAELoad/Interaction</td><td>Units</td><td>Description</td></tr><tr><td>R</td><td>Surface radiation</td><td>Dimensionless</td><td>Emissivity and sink temperature (units of θ) provided on the element surface.</td></tr></table>

# Element output

Element output is always in the global directions.

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# All elements

![](images/page-208_d8d93d818c000807c53c6103a4a237a9e250767e090353d8076dfa1571932e36.jpg)

<details>
<summary>text_image</summary>

face 2
face 4
face 3
1
2
3
face 1
</details>

4 - node element

![](images/page-208_e9dbc14a12c5ab3df53b7234ad2406067d4b20ef51c4c04590d3c3ab3b3cbaf7.jpg)

<details>
<summary>text_image</summary>

5
face 4
face 5
4
face 3
3
1
face 1
2
face 2
</details>

5 - node element

![](images/page-208_55b8ef7de7029edd06269fec73bc2743243752d3077eac482291047fe70fd00c.jpg)

<details>
<summary>flowchart</summary>

Face diagram structure diagram showing connections between labeled faces and a central node, with directional arrows indicating flow or relationships.
</details>

6 - node element

![](images/page-208_6add88f144f6fbdf64c13a5b54e1d276799c06aec459af1420bc3b21ee9c5e4a.jpg)

<details>
<summary>text_image</summary>

face 2
8
face 5
7
face 6
4
3
face 4
5
6
1
face 1
2
face 3
</details>

8 - node element

![](images/page-208_4dab637153b964f3bfda3565e9d2686c8496dc7e8194d331571fe4cc1a59cf88.jpg)

# Tetrahedral element faces

Face 1 1 – 3 – 2 face

Face 2 1 – 2 – 4 face

Face 3 2 – 3 – 4 face

Face 4 1 – 4 – 3 face

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Pyramid element faces 

<table><tr><td>Face 1</td><td>1-4-3-2 face</td></tr><tr><td>Face 2</td><td>1-2-5 face</td></tr><tr><td>Face 3</td><td>2-3-5 face</td></tr><tr><td>Face 4</td><td>3-4-5 face</td></tr><tr><td>Face 5</td><td>1-5-4 face</td></tr></table>

Wedge (triangular prism) element faces 

<table><tr><td>Face 1</td><td>1-3-2 face</td></tr><tr><td>Face 2</td><td>4-5-6 face</td></tr><tr><td>Face 3</td><td>1-2-5-4 face</td></tr><tr><td>Face 4</td><td>2-3-6-5 face</td></tr><tr><td>Face 5</td><td>1-4-6-3 face</td></tr></table>

Hexahedron (brick) element faces 

<table><tr><td>Face 1</td><td>1-4-3-2 face</td></tr><tr><td>Face 2</td><td>5-6-7-8 face</td></tr><tr><td>Face 3</td><td>1-2-6-5 face</td></tr><tr><td>Face 4</td><td>2-3-7-6 face</td></tr><tr><td>Face 5</td><td>3-4-8-7 face</td></tr><tr><td>Face 6</td><td>1-5-8-4 face</td></tr></table>

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