Configuring Energy Coupling Between Regions

For CHT simulations where the same timescale applies in both regions, you can use an implicit solution procedure that solves equations in both regions simultaneously. When the timescales differ, however, you must solve equations in each region consecutively. For this reason, an explicit mapped interface is required that can also provide time-averaged data to the solid side.

The energy coupling is achieved using an explicit mapped contact interface where the Boundary Heat Flux and by default the Specified Y+ Heat Transfer Coefficient at Y+ = 100 are exchanged across the interface. The fluid region sees the static temperature on the solid region, while the solid region receives convection data from the fluid side.

To define the explicit mapped contact interface:

Select the Interfaces > Exhaust Gas/Manifold Solid node and set Type to Mapped Contact Interface.
Select the Interfaces > Exhaust Gas/Manifold Solid > Physics Conditions > Energy Coupling Option node and set Energy Coupling Option to Explicit.

Additional setup is required to determine which type of data each region receives through the interface. You specify this behavior on the boundaries on either side of the interface:

Select the Regions > Exhaust Gas > Boundaries > Faces [Exhaust Gas/Manifold Solid] > Physics Conditions > Time Averaging Option node and set Option to Instantaneous.
Instantaneous indicates that the thermal data from the solid side is mapped across the explicit interface to this boundary without being time-averaged. As the temperature of the solid changes at a much slower rate than that of the fluid, the instantaneous value is sufficient.
Select the Regions > Manifold Solid > Boundaries > Faces [Exhaust Gas/Manifold Solid] > Physics Conditions > Time Averaging Option node and set the Option to Sliding Window Average.

Select the Physics Value > Time Averaging Parameters node and set the properties as follows:

Property

Setting

Sliding Sample Window Size

720

Sampling Delta Time

${FluidTimeStep(s)}

Note	This setting means that the rolling average is updated with a sample every 2 deg CA.

With the Time Averaging Parameters defined above the boundary heat flux and heat transfer coefficient from the fluid side are averaged before being mapped across the explicit interface.

You set the outer wall boundary Faces of the solid region to a Convection thermal condition.

Select the Regions > Manifold Solid > Boundaries > Faces node and set the following conditions:


Node	Property	Setting
Physics Conditions
Thermal Specification	Condition	Convection
Physics Values
Ambient Temperature	Value	360 K
Heat Transfer Coefficient	Value	6.667 W/m^2-K

Save the simulation.