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logarithmic profile velocity - inlet BC

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Old   June 14, 2013, 09:58
Unhappy logarithmic profile velocity - inlet BC
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Pedro Ramos
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Hello Openfoamers,

I want to define a logarithmic velocity profileto my open channel flow (like this:
What do you suggest? Groovy BC? I have some problems to install it with OF 2.0.

There is a simpler way?

Best regards,
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Old   June 14, 2013, 15:06
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If you are working with a RANS turbulence model, you should be able to use the atmBoundaryLayerInletVelocity which simply imposes the logarithmic velocity profile.

Cheers,

L
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Old   June 15, 2013, 05:09
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hi pedro,

What about expanding the log and using codedFixedValue (Getting errors on compiling boundary condition) , as i am a newbie my knowhow is limited too. Expect this may help
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Old   June 15, 2013, 11:25
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@Pedro: OpenFOAM 2.0 or 2.2.0?
Quote:
Originally Posted by pedroxramos View Post
Groovy BC? I have some problems to install it with OF 2.0.
If it's OpenFOAM 2.2.0, read the instructions on this post: Error installing swak4Foam post #16

Best regards,
Bruno
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Old   June 17, 2013, 05:08
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Hello.

Thanks. Yes, It's OF 2.2.0. I'll try install it and input the log profile with swak4foam.

Regards,
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Old   June 17, 2013, 05:30
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Quote:
Originally Posted by Lieven View Post
If you are working with a RANS turbulence model, you should be able to use the atmBoundaryLayerInletVelocity which simply imposes the logarithmic velocity profile.

Cheers,

L
Thanks, but I'm using InterFoam with LES model.
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Old   June 17, 2013, 10:49
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Ok, completely different situation.

The logarithmic velocity profile is the profile a time averaged profile. This profile does not exist as instantaneous profile so it is physically not correct to impose the log-profile directly at the inlet.

the most correct thing to do is use an 'infinite inlet' to generate profiles which result in the log-profile when they are time averaged. Two ways to do this:
1. Do a separate simulation of a cyclic channel and store every inlet
2. Increase the length of the inlet and use the mapped BC at the inlet.

Cheers,

Lieven
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Old   June 19, 2013, 06:06
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Quote:
Originally Posted by Lieven View Post
Ok, completely different situation.

The logarithmic velocity profile is the profile a time averaged profile. This profile does not exist as instantaneous profile so it is physically not correct to impose the log-profile directly at the inlet.

the most correct thing to do is use an 'infinite inlet' to generate profiles which result in the log-profile when they are time averaged. Two ways to do this:
1. Do a separate simulation of a cyclic channel and store every inlet
2. Increase the length of the inlet and use the mapped BC at the inlet.

Cheers,

Lieven
Hi Lieven, thanks for your help.

Which boundary condition should I put in the bed to to the second suggestion that you gave me? I put the no slip condition, like this:

bed - U
{
type fixedValue;
value uniform (0 0 0);
}

U.txt

And the contour of the velocity in the midplane of the channel is: http://d.pr/i/ZWvo


The distance between the inlet and the pille is 1 meter. Should I keep the bed boundary condition and increase that distance?

Best regards.
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Old   June 19, 2013, 08:22
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Hi Pedro,


You should use the 'mapped' boundary condition for that. Have for example a look at
mapped boundary condition
If you google a bit or search this forum, I'm sure you will find more information on it if the link about is not enough.

Cheers,


Lieven
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