[agodfrey]

An FYI,

Given:

A custom field function: d-area = abs(x_face_area)
Reports: Surface Integrals
Report Type: Sum
Field Variable: Custom field functions
darea (defined as abs(x-face-area) )
Surfaces: A defined constant-x plane cut through the domain

Yields: Zero erroneously

Other information:

Writing the data shows that each face equals zero to machine precision.

Report Type: Area yields the correct (non-zero) area.

Report Type: Integral w/Custom Fields Function unity (defined as 1) also yields the correct area.

Report Type: Sum on a boundary surface yields the correct area.

Conclusion: Using Sum with a custom field function which needs x-area-face on a defined surface yields erroneous results. Use Report Type: Integral instead.

Note: the integrand of interest is actually (rho * Vx ^ 2 * d-area)