In CFX you can set the expert parameter ‘skew diffusion scheme=3’ In Fluent, the equivalent to the CFX parameter is to type (rpvar ‘temperature/secondary-gradient? #f) in the Fluent TUI. This setting drops all nonorthogonal diffusion contributions, which is less accurate (zero-order) for skewed cells, but more robust/bounded. An alternative workaround, which does something like this at just the boundaries/interface, is to type “solve set expert” in the TUI and to answer ‘yes’ to the first question (‘use alternate formulation for wall temperatures?’.) This second option might be better, as it affects only the interface connection.