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-   -   Good Cp using air, but wrong if using water (https://www.cfd-online.com/Forums/openfoam-solving/121428-good-cp-using-air-but-wrong-if-using-water.html)

Baldy July 28, 2013 16:20
Good Cp using air, but wrong if using water
 
I am simulating a fluid jet impacting a wall. I get the correct pressure coefficient (Cp) distribution on the wall when using air.

When I try simulating it with water at the same Reynolds number, the Cp distribution is correct, however the value is off by a factor of 200.

I have double checked that I am using the proper velocity and rho for calculating the Cp, but I can't figure out why I'm getting so low Cp.

Artur July 29, 2013 03:15
By wrong Cp distribution do you mean wrong forces output or incorrect pressure values when viewed in paraview?

Baldy July 29, 2013 17:41
The Cp distribution is correct (looks like a bell curve), however the pressures given in Paraview are too low.

Baldy August 5, 2013 19:55
UPDATE
If I calculate the pressure coefficient using the surface pressure I got with the water and use rho_air, my results are good.

This is what my transportProperties look like:

Code:
transportModel  Newtonian;

nu              nu [0 2 -1 0 0 0 0] 1.004e-06;
DT                DT [0 2 -1 0 0 0 0] 1.439e-07;

Is there a reason why OpenFOAM would use nu_air even if I defined the one for water? I'm using icoFoam with temperature added.


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