5.2.1.2. Bulk Node Example

A bulk node provides a method for tracking the temperature in a non-meshed region in the problem. This could be an external environment, or an internal cavity filled with a fluid of some kind. A bulk node adds a single DOF to the overall equation system and the surfaces tied to the bulk node can exchange energy convectively.

Because bulk nodes can use the convective correlation library, using a bulk node with an extremely large volume as the ambient condition allows the use of the correlation library for not only internal surfaces but also those convecting to an external ambient environment.

5.2.1.2.1. Problem Files

The files required for this example can be downloaded here, or found at $TESTS/aria_rtest/example/training/bulkelem (where TESTS=/projects/sierra/tests in a CEE environment, or your Sierra test distribution otherwise).

Input File

Mesh

5.2.1.2.2. Input Deck Modification

To add a bulk node to an Aria problem, you need to make the following changes:

Add a material to use in the bulk node. At a minimum, this material should define the necessary properties to solve an energy equation on the bulk node (density and specific heat). If using a correlation for the convection coefficient, additional properties may be required.
Begin Aria Material air
    Density       = Constant value = 0.972  # kg/m^3
    Specific Heat = Constant value = 1004.2 # J/kg-K
End
Add a Bulk Fluid Element block in the Aria region and specify the material to use on it, its initial temperature, the equation to solve, and how to calculate the bulk node volume. The volume can either be computed automatically from the bounding surfaces of the bulk node (defined based on which boundary conditions are linked to this specific bulk node) or specified manually using Bulk Element Volume = Constant v = 1.23 in the Bulk Fluid Element block.
# Aria Region
Begin Bulk Fluid Element air_void
    Calculate Volume from Enclosing Surface
    Material = air
    Initial Temperature = 300.0 # K
    Bulk EQ Energy for Temperature Using P0 with Mass
End   Bulk Fluid Element air_void
Link convection boundary conditions to the bulk node. If the bulk node volume is calculated from its enclosing surfaces, those are determined based on which boundary conditions are linked to the bulk node. Boundary conditions can be changed from flux type to bulknode_flux type. The convection coefficient can either be supplied as an in-line string function, using the heat transfer coefficient property in a surface material, or using a correlation. When using a correlation, specify which correlation block to use using the hcorr argument.
BC Bulknode_Flux for Energy on bulk_node_surfs = Generalized_Nat_Conv \$
    bulk_node = air_void \$
    h = 10.0
BC Bulknode_Flux for Energy on bulk_node_surfs = Generalized_Nat_Conv \$
    bulk_node = air_void \$
    hcorr = my_convection_correlation
The boundary condition can also be set using a block-style syntax
Begin Convective Flux Boundary Condition conv_to_void
    Add Surface bulk_node_surfs
    Convective Coefficient = 10.0
    Use Bulk Element air_void
End