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Error in mass flow rates in inlet region of pipe during pipe flow simulation

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Old   September 20, 2019, 14:10
Default Error in mass flow rates in inlet region of pipe during pipe flow simulation
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I am simulating laminar flow in a circular pipe (medium is water: density 998.2 kg/m3, viscosity = 0.001003 kg/m-s), in Ansys Fluent 16.0
The boundary conditions are:
at inlet: velocity is 0.1 m/s
at outlet: pressure is 20 bar

the diameter of pipe is 4.6mm and the lenght of pipe is 550mm.

after running the simulation, in the post processing, the massFlow calculator gives:
massflow at Inlet : 0.00165708328 kg/s
massflow at Outlet: -0.00165708328 kg/s

the outlet and inlet were defined during Geometry creation in ICEM-CFD.

However, when defining new planes (in CFD-Post), at location x=0mm, x=1mm etc, I obtain different values, (which i have mentioned in an attached text file)

Please note that inlet is at x=0mm, and outlet at x=550mm
I get about 1.5% difference in mass flow at x=0mm.

my question is, why is Inlet(defined in ICEM) and plane x=0mm showing different mass flow rates (using massFlow calculator)
Attached Files
File Type: txt massflow13.txt (2.6 KB, 4 views)
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Old   September 22, 2019, 14:04
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There is a difference between the calculations done by the solver and cfd post to get the results. ghorrocks wrote about it in this thread: Monitor Point expression value different from same expression in CFX-Post

Also I think you are in the wrong subforum, at least your name indicates you are a Fluent user. This is the CFX forum. Nevertheless, I think the same explanation is valid for Fluent solver and CFD post.
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