Multiphysics > Coupling to external CFD solvers

Exchanging data between solvers at coupling time

Data is exchanged between the thermal solver and the external CFD solvers only on the regions where you define the following loads:

Thermal Stream
Thermal Convecting Zone

Mapping data

The software needs to map data between solvers. Data on the two models is defined on different meshes and locations. The following table summarizes the mapping process depending on data location.

Source data location	Target data location	Mapping process
Elements	Elements	The software assigns elemental data of the source element that is closest to the target element.
Elements	Nodes	The software assigns elemental data of the source element that is closest to each target node.
Nodes	Elements	The software interpolates nodal data of the source element that contains or is closest to the center of gravity of the target element and assigns the interpolated value to the target element.
Nodes	Nodes	The software interpolates nodal data of the source element that contains or is closest to the target node and assigns the interpolated value to the target node.

Data exchange: external CFD solver→thermal solver

The thermal-flow quantities are transferred from the external CFD solver to the thermal solver through CFD coupling functions that you specify as expressions in appropriate boundary conditions. For each CFD coupling function, you specify the External Solver modeling object name (), the name of the corresponding boundary condition in the external CFD model (), and, optionally, the location of the external CFD results (). The last argument can be either "ELEMENTS" or "NODES". If it is not defined, the source results are assumed to be elemental. This argument is used to map results between the solvers.

The following table lists the CFD coupling function for each wall variable that can be transferred from the CFD solver to the thermal solver through a Thermal Convecting Zone load.

Variable name	CFD coupling functions	Description	Field name in the Thermal Convecting Zone dialog box
Fluid temperature	cfdcoupl_wall_fluidtemp(,,)	The value of the convecting zone fluid temperature is computed by the external CFD solver.	Environment group→Temperature
Wall static pressure	cfdcoupl_wall_pressure(,,)	The value of the convecting zone wall static pressure is computed by the external CFD solver.	Environment group→Pressure
Heat transfer coefficient	cfdcoupl_wall_htc(,,)	The value of the convecting zone heat transfer coefficient is computed by the external CFD solver.	Heat Transfer group→Heat Transfer Coefficient
Heat flux	cfdcoupl_wall_heatflux(,,)	The value of the convecting zone heat flux is computed by the external CFD solver.	Heat Transfer group→Heat Flux

The following table lists the CFD coupling function for each inlet/outlet variable that can be transferred from the external CFD solver to the thermal solver through a Thermal Stream load.

Variable name	CFD coupling functions	Description	Field name in the Thermal Stream dialog box
Mass flow	cfdcoupl_io_massflow(,<CFD inlet/outlet name>,)	The value of the stream mass flow is computed by the external CFD solver.	Stream Conditions group→Mass Flow
Absolute mass averaged temperature	cfdcoupl_io_abstemp(,<CFD inlet/outlet name>,)	The value of the stream inlet temperature is computed by the external CFD solver. The absolute mass averaged temperature is used as the inlet temperature.	Stream Conditions group→Inlet Temperature
Inlet or outlet static pressure	cfdcoupl_io_pressure(,<CFD inlet/outlet name>,)	The value of the stream static pressure is computed by the external CFD solver.	Stream Conditions group→Pressure
Swirl velocity	cfdcoupl_io_swirlvel(,<CFD inlet/outlet name>,)	The value of the stream swirl velocity is computed by the external CFD solver.	Heat Transfer group→Swirl Velocity Heat Transfer - Side A group→Swirl Velocity Heat Transfer - Side B group→Swirl Velocity

Data exchange: thermal solver→CFD solver

If the convecting zone has at least one CFD coupling function defined, the thermal solver transfers solid temperature results of the Thermal Convecting Zone regions to the external CFD solver at each coupling time.

When you define an External Solver Boundary Condition simulation object, you can also transfer any or all of the following quantities to the specified boundary condition of the external CFD model:

Fluid temperature, pressure, and mass flow
Rotational speed and swirl velocity
Heat pickup
Gap distance
Length and unitless quantity

These quantities can be constant or time-varying or you can use auto-generate expressions to define them.

How do I

Define external CFD solvers

Define transfer of CFD data to the thermal solver

Define boundary conditions for external solvers

Learn more

Coupling to external CFD solvers

Simcenter 3D Multiphysics workflow: coupled thermal-structural analysis with an external CFD solver

External Solver Boundary Condition

Thermal Convecting Zone

Thermal Stream

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

Browse Simcenter 3D help by product area