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

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FC 3D 4 number of nodes three-dimensional fluid continuum

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. # 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

FC3D4	4-node tetrahedron
FC3D5	5-node pyramid
FC3D6	6-node prism
FC3D8	8-node brick

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

Input File Usage:	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
Abaqus/CAE Usage:	In Abaqus/CAE you can only define the element properties for flows.Property module:Create Section:select Fluid as the section

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

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

# 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.

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

# 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.

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

# 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.

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

# 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.

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

# Element output Element output is always in the global directions. # All elements 

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face 2 face 4 face 3 1 2 3 face 1

4 - node element 

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5 face 4 face 5 4 face 3 3 1 face 1 2 face 2

5 - node element 

flowchart

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

6 - node element 

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face 2 8 face 5 7 face 6 4 3 face 4 5 6 1 face 1 2 face 3

8 - node element  # 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 Pyramid element faces

Face 1	1-4-3-2 face
Face 2	1-2-5 face
Face 3	2-3-5 face
Face 4	3-4-5 face
Face 5	1-5-4 face

Wedge (triangular prism) element faces

Face 1	1-3-2 face
Face 2	4-5-6 face
Face 3	1-2-5-4 face
Face 4	2-3-6-5 face
Face 5	1-4-6-3 face

Hexahedron (brick) element faces

Face 1	1-4-3-2 face
Face 2	5-6-7-8 face
Face 3	1-2-6-5 face
Face 4	2-3-7-6 face
Face 5	3-4-8-7 face
Face 6	1-5-8-4 face