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Old   April 25, 2011, 16:41
Red face Additional Variable
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Timothy
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I hope this is not a stupid question

(CFX 12.1)

I need to use the negative of the gradient of wall distance as an input to a particle tracking routine. CFX has the variable wall distance and I would like to define an additional variable for the negative gradient of the wall distance. In CFX pre I can click on the additional variable button and I can specify the variable type, the units, and the tensor type. I do not understand how I can cause the variable to be equal to the negative gradient of the wall distance. Where do I specify this?

Also I assume that the tensor type will be a vector. Should the variable type be unspecified and the units be [m]?

Or should I be using additional variable at all?

Thanks in advance,
tim
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Old   April 26, 2011, 21:56
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Glenn Horrocks
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I think the variable you want is "Wall Distance". It is a scalar, not a vector.
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Old   April 28, 2011, 11:25
Cool I figured out some things
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In case someone is having the same issue some time:

First of all the way you actually define what an additional variable is equal to, is in Default Domain/Fluid Models/Additional Variable Models. I was not really expecting that

I agree that wall distance is a scalar, however, the negative gradient of the wall distance is a vector. I was wrong about the units because if you have something with the units [m] the gradient of that is dimensionless. I think that the type should still be unspecified but I am still not really sure what that does.
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Old   April 28, 2011, 12:33
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Quote:
Originally Posted by tav98f View Post
In case someone is having the same issue some time:
I agree that wall distance is a scalar, however, the negative gradient of the wall distance is a vector.

Thanks Tim that was useful.
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