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-   -   SimpleFoam Laminar Pipe Flow Pressure Drop Error (https://www.cfd-online.com/Forums/openfoam-solving/220607-simplefoam-laminar-pipe-flow-pressure-drop-error.html)

 xiaolong September 13, 2019 09:10

SimpleFoam Laminar Pipe Flow Pressure Drop Error

Hello Foamers,

I am new to openfoam. I am trying to simulate a laminar pipe flow by using simpleFoam and compare the pressure drop with the analytical solution. However, I found a quite consistent about 11% pressure drop error by adjusting the inlet velocity (Re=500, 1000, 1500, 2000)

Below are the parameters I used for this simulation

Pipe length (L): 0.5m
Pipe diameter (D): 0.015m
Dynamic viscosity (mu): 8.9e-4 N/m-s
Density (rho): 997 kg/m^3
Max value of parabolic velocities:
(1) 5.96e-2 m/s(Re=500); (2) 1.19e-1 m/s (Re=1000); (3) 1.78e-1 m/s (Re=1500); (4) 2.38e-1 m/s (Re=2000).
Boundary conditions:
p:
Outlet: fixedValue uniform 0;
U:
Inlet: parabolic velocity (I tried fixedvalue uniform inlet velocity as well without measuring in the entry length region, the same problem);
Wall: fixedValue uniform (0 0 0);

I also compared simulation results with Fluent, as shown in the figure below:

https://www.dropbox.com/s/22xv8hlwuv...luent.png?dl=0

I have tried (1) refining the mesh in different levels; (2) adjusting the gradient scheme to leastsquares method; (3) importing the mesh developed in ANSYS for Fluent simulation. None of these can change the results.

Since this is a very simple case, I believe simpleFoam should be able to provide accurate prediction on the pressure drop. However, I just can not get it.

I really appreciate if anyone can help to point out what the problem is.

https://www.dropbox.com/s/w91ak3klx3..._flow.zip?dl=0

Thanks,
Xiaolong

 xiaolong September 16, 2019 09:26

Anyone has some insight in this?

 Bloerb September 16, 2019 10:57

Your viscosity in transportProperties ("1e-06; //water")

does not match what you specified
Code:

```Dynamic viscosity (mu): 8.9e-4 N/m-s Density (rho): 997 kg/m^3```

 xiaolong September 16, 2019 11:37

Quote:
 Originally Posted by Bloerb (Post 744796) Your viscosity in transportProperties ("1e-06; //water") does not match what you specified Code: ```Dynamic viscosity (mu): 8.9e-4 N/m-s Density (rho): 997 kg/m^3```
Hi Bloerb,

Thank you very much. I didn't realize I messed up with my data. Now it's matching.

Best,
Xiaolong

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