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February 20, 2014, 17:52 
Match mass flow rate with inlet pressure and outlet pressure

#1 
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Hi all,
I try to simulate the flow through a pipe (L/D=100). I set an inlet pressure (inlet circular section of the pipe) and an outlet pressure boundary condition (outlet circular section). Unfortunately, the mass flow rate computed does not match the one measured experimentally!!! Have you an idea to solve it? The problem is quite fundamental, I suppose. Thanks, 

February 20, 2014, 18:42 

#2  
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Filippo Maria Denaro
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Quote:


February 21, 2014, 07:13 
Details of the simulation

#3 
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Dear Denaro,
The geometry considered is very simple. A pipe Length = 100 x Diameter. The inlet pressure is 3 bar and the outlet is atmosphere (thus, I set a pressure outlet of 0 bar). I choosed laminar as viscous model because there is no turbulence in this configuration. However, the computed mass flow rate does not match the experimental value. Tell me if you need more details. 

February 21, 2014, 07:51 

#4 
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Filippo Maria Denaro
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You said nothing about your computational setup.
For laminar pipe flow You have an analytical solution to check for, have You already tested? 

February 21, 2014, 09:06 

#5 
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I compared the results given by Fluent and the analytical value. They are different!
My computational setup is simple: laminar as viscous model, second order, 10e6 as residual. 

February 21, 2014, 09:46 

#6 
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Filippo Maria Denaro
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what about the formulation you chose?
has the streamwise velocity developed a parabolic profiles? Do the other velocity components vanish? 

February 21, 2014, 10:18 

#7 
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I understand what you mean.
In fact, the length of the tube is not long enough to obtain a fully developed HagenPoiseille flow. The pressure drop is almost linear. However, the mass flow rate obtained is not equal to that measured. To go further, the configuration above is a preliminary test for a more complex geometry I have to simulate: A flow through three successive cylinders called three disks.  The first and the third one have small diameters but the second one has a big diameter (ten times).  I have experimental data and I realized that Fluent do not give good results in terms of mass flow rate.  Let's consider that a bc pressure inlet (3 bar) and a bc pressure outlet (0 bar) are applied. I used a RNG kepsilon as viscous model. That's would be great if you have some excellent ideas Thanks in advance 

February 21, 2014, 10:24 

#8 
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Filippo Maria Denaro
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I still can not understand your setup... Laminar flow and keps model????


February 21, 2014, 13:52 

#9 
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What are you using for your analytical solution? What Re are you running at?


February 21, 2014, 19:07 

#10 
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This is the setup (I guess):
Symmetry Boundary Condition Question: you said your inlet pressure is 3bar and your outlet pressure is the ambient pressure and you set it at 0bar. Now, actually the ambient pressure is 1bar. Your setup is ok as long as your inlet pressure is relative to ambient pressure otherwise you might be missing a bar. 

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