Rob
Ansys Employee

https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v222/en/flu_udf/flu_udf_DataAccessMacros.html

You want the TUI command from just above Table 3.11 and Section 3.2.11.3   

And also https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v222/en/flu_udf/flu_udf_FluentDataTypes.html