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-   -   Initialization problem in open channel flow simulation (https://www.cfd-online.com/Forums/star-ccm/151471-initialization-problem-open-channel-flow-simulation.html)

swtbkim April 11, 2015 08:18

Initialization problem in open channel flow simulation
 
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Hi all.

I'm analyzing a propeller in a tank. I attached simple schematic figure.

Behind the propeller is a pipe, so air will be sucked because of a negative pressure there and rise to the surface.

I made a field function for a hydrostatic pressure distribution
--> hydro distribution = ($$Position[1]<=1)?{$$DensityofWater}*9.81*(1-$$Position[1]):0 (i.e. reference altitude is y=1.0m and gravity acts along -y direction)

Problem is that I can not initialize the hydrostatic pressure. star-ccm+ gave me an error.
"Unable to compute field function a hydrostatic pressure on "region", Please check that function is defined here"

If I don't initialize the pressure, then hydrostatic pressure distribution should be calculated in solver and it will take too long, and it didn't even converge.

I'm using MRF and multiphase - VOF.


Thank you in advance!

fluid23 April 13, 2015 16:35

I have have seen it do something similar resulting from poorly defined region names that had extra '.' separators in the region name. So if I had a region named 'Region' and a boundary named 'Boundary One' I named it as 'Region.Boundary.One' So it was looking for a region boundary named Boundary not Boundary.One. It doesn't appear that this is your problem though.

I will say that it looks like maybe your DensityofWater field function maybe defined or called wrong. Perhaps I am mistaken, but I thought that a double $$ is for a vector, not a scalar.

Also, have you tried expert initialization (grid sequencing)? That has cut (literally) days off my analyses in the past. It isn't always appropriate, but when it works it works well.


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