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Chris January 5, 2007 06:22

Pressure loss in pipe
 
Hi guys and girls;-)

I'm going an investigation of fully developed laminar air flow in a horizontal pipe (using periodic boundaries and creating a subdomain and defining a general momentum source in the z-direction) in ANSYS CFX 10.0.

I'm trying to determine the pressure loss through the pipe using the table viewer in CFX-Post but the results don't match the ones I have calculated theoretically.

Here is what I have inserted in the table viewer:

areaAve(ptot )@Domain Interface 1 Side 1 - areaAve(ptot )@Domain Interface 1 Side 2

Any idea as to why the pressure from the table viewer doesn't comply to the theoretically calculated?

Ps. I have checked that I get a laminar velocity profile " although I find that I need a Reynolds number at about 25-70 in order the match the theoretical profile. If I use larger Reynolds numbers i.e. 1000 I get a much more turbulent looking profile which surprises me as normally laminar flow presides in pipe flow until RE = 2300.

Any ideas or comments about something I could be doing wrong are welcome...:)

Regards Chris


Robin January 5, 2007 12:04

Re: Pressure loss in pipe
 
Hi Chris,

You need to add in the effect of the momentum source you used to drive the flow, it will not be included in the pressure. Actually, since you are prescribing the pressure drop, you should compare the mass flow and velocity profile to the theoretical values for the pressure drop you have prescribed.

If you still don't acheive the same results, run again with progressively finer meshes. Eventually the numerical dissipation due to the mesh resolution should be reduced to the order of the roundoff error.

Regards, Robin


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