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"du/dy" by "CEL" expression

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Old   September 14, 2011, 19:44
Default "du/dy" by "CEL" expression
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sajad
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hi all.
i want to calcuate derivative of u velocity with respect to normal cordinate.i mean that i want "du/dy".
is it possible to use "CEL" expression to obtain this quantity?
best regards.
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Old   September 14, 2011, 23:25
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Glenn Horrocks
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u.Gradient y
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Old   September 18, 2011, 10:53
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sajad
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hi Glenn
can i use this formula "u.gradiant y" in pre processing?
i want to set it as a boundary condition.i mean that my B.C is in dependent of "du/dy".
so can i define CEL expression and use it as B.C?

best regards.
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Old   September 18, 2011, 18:24
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Can you explain what you are doing? Openings and outlets already set du/dy (normal to the interface) to zero.
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Old   September 19, 2011, 10:07
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sure.
i want to set slip velocity condition on walls and the formula is the maxwell-smoluchowski first order slip condition in this form:
us-uw=((2-alfa)/alfa)*landa*du/dy
so i need to have u gradient with respect of y on walls.
is it possible to do this with writing "CEL" expression?
thanks.
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