Volume Flow Rate and Area * Velocity values different
Hello,
I have a fluent model, where the fluid is of constant density. Structured mesh, well converged. But the volume flow rate what fluent shows is different when I multiply the area and area weighted average of velocity magnitude. Did not understand ? Why ? (Volume Flow Rate) Fluent != (Area) fluent * (Area weighted average of velocity magnitude) fluent Thanks in advance 
Is it multiphase?

No .... the fluid is air

That sounds strange... How much do they differ?

Ahh maybe this:
What do you integrate for the "Area weighted average of velocity magnitude"? You need to integrate only the perpendicular (to the surface) component of the velocity vector  not the length of the complete velocity vector! 
(Volume Flow Rate) Fluent == (Area) fluent * (Area weighted average of normal component of velocity) fluent
Note the difference between <vector u> dot <vector A> and magnitude u*magnitude A. 
I tried with Velocity magnitude, X, Y and Z velocities .... still they differ.
When I calculate velocity = (volume flow rate/area) fluent and area weighted avg of (velocity magnitude/Xvel/Yvel/Zvel), both differ by almost 45m/s 
But this isn't what I wrote:
You need the perpendicular velocity component. If your surface is no "simple" cartesian surface, the cartesian (x,y,z) components won't help you. What you need is "A dot v"! 
It is a simple rectangular surface. So don't you think the velocity magnitude is normal to that ?

Not necessarily... Why don't you post pictures?

Let the normal of the rectangle be [nx, ny, nz], and the areaweighted average of x,y,z velocity be [U, V, W], then (U*nx + V*ny + W*nz) should not be differ much from the volumetric flow rate divided by the area.

Thanks !
Will do that. 
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