How to Visualize the "Mapped Averaged Reference Temperature" and "Mapped Averaged Specified Y+ Heat Transfer Coefficient" Field Functions When Using an Explicit Mapped Contact Interface

For certain powertrain applications that require explicit coupling between fluid and solid thermal simulations (such as exhaust manifold, piston cooling, e-motor cooling, brake cooling, etc.), the implicit mapped contact interface is typically used. This interface allows for the mapping of heat transfer coefficient and reference temperature from the fluid to the solid, and then mapping the temperature from the solid back to the fluid.

When conducting transient fluid simulations, an averaging method is usually necessary to average the heat transfer coefficient and reference temperature from the fluid side. This can also be achieved using the mapped contact interface, by enabling the "Sliding Window Average" under the "Time Averaging Option".

This will enable the use of the "Mapped Averaged Reference Temperature" and "Mapped Averaged Specified Y+ Heat Transfer Coefficient" field functions by default for mapping on the solid-side interface.

As a user, you may want to visualize these two field functions to ensure that they provide reasonable values. It is also important to check if they are limited to certain values, as the defined specified Y+ value (default  is100) may not be available for low velocity area. 

First, it's important to note that we actually map the averaged boundary heat flux (q) and averaged heat transfer coefficient (h) from the fluid to the solid side. The averaged reference temperature (Tref) is then computed during the first iteration of the solid cycle, using the formula:

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where Tw is the temperature at the solid interface boundary during the first iteration. All subsequent iterations will continue to use these values of h and Tref.

For visualization purposes, q is available as "Time Averaged Boundary Heat Flux" on the fluid interface boundary, while "Mapped Averaged Specified Y+ Heat Transfer Coefficient" and "Mapped Averaged Reference Temperature"  ​are available as "External Heat Transfer Coefficient" and "External Ambient Temperature" on the solid interface boundary.