This might be done through Report Definitions. A report definition is an object that specifies a certain quantity or set of values to be computed at the end of a solver timestep or iteration. For example, the surface integral of pressure in a set of boundaries could be created as report definition. Report definitions are also available for use in custom field functions (Custom Field Functions). That means one can use the report definitions to calculate directly the total pressure loss across a duct for example. 1/Create Report Definition for area weighted average of Total Pressure @ inflow boundary 2/Create Report Definition for area weighted average of Total Pressure @ outflow boundary 3/Create a Custom Field Function as difference between the above defined Report Definitions 4/Now we need just to evaluate the Customer Field Function. This might be done via the creation of a third Report definition or using a classical Surface or volume integrals or just computing the range value of the custom field function in the Contours panel See also chapter “29.16. Report Definitions” in the ANSYS Fluent 17.x User’s Guide.