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[ICEM] Simple pipe meshing - problems with y+ in CFX

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Old   December 1, 2012, 15:27
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Far
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Sijal Ahmed Memon (turboenginner@gmail.com)
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will 6.7 m/sec make the difference or velocity profile is the main culprit What will happen if I use 10 m/sec?


Did you take care of axis direction? Can you share the velocity profile?
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Old   December 1, 2012, 15:51
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Quote:
Originally Posted by Keizers View Post
1.0 I had used was 6.7m/s

2.0 Another thing I recall I may have different is the blending factor in the outlet (is it called that? sorry, I can't remember). There are two values you need to fill when you choose average static pressure as BC, the pressure itself and a factor. I have that as 0.05, as it is in the tutorial of the valve.

3.0 And finally, I have noticed you are doing it from within workbench, whereas I was doing it directly in CFX. But surely there is no difference there?


K
1. With 6.7 m/sec, maximum Y+ = 0.35

2. see this Average static Pressure If you specify blending factor = 1 then is same as uniform static pressure.
I have also used blending factor = 0.05

3. Using from workbench or directly doesn't make difference.

Some text from CFX help:
Quote:
he Pressure Profile Blend is a measure of enforcement of the specified pressure profile to the outlet boundary. For example, using a blend of 0.0 specifies no enforcement of the pressure profile. In this case, the behavior of the Scale Mass Flows method is recovered. A blend of 1.0 fully imposes the pressure profile shape (but not the level) as well as the mass flow leaving the domain.
blending factor = 0 ~ mass flow rate option
blending factor = 1 ~ uniform static pressure.

Try to use the blending factor = 1.0 and see what happens.

Last edited by Far; December 1, 2012 at 16:27.
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Old   December 2, 2012, 17:55
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Hi Far,

I have run it again. And it WORKS. In fact, my previous meshes work too (although yours gives better y+, mine have y+ of around 100, but that is a matter of refining, and much better than 150,000!). I am embarrased to admit the mistake I was making. Let's just say it was something very very dumb.

I have looked up the blending factor now, sorry, I didn't have the helpfiles when I wrote my previous message. I will try changing it to 1 later, but since things work now it is not a problem.

the velocity profile I use is:
Wmax*(abs(1-r/Rmax)^0.143)
where Wmax=8.197m/s
Rmax=20mm

and that goes in the W box in the inlet when choosing cartesian velocity components.

Thanks so much for all your help. It was this last bit of checking what was different to your simulation that allowed me spot the mistrake. Thank you.

K
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Old   January 15, 2015, 09:00
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dear Keizers

so i have work similar to your case (circulair pipe two phase flow), i want to put new wall function in CFX , just you can say that im new in cfx , can you send me your case or simple one to begin. thanks
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