"du/dy" by "CEL" expression

sajad_abasi · September 14, 2011, 19:44

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.

ghorrocks · September 14, 2011, 23:25

u.Gradient y

sajad_abasi · September 18, 2011, 10:53

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.

ghorrocks · September 18, 2011, 18:24

Can you explain what you are doing? Openings and outlets already set du/dy (normal to the interface) to zero.

sajad_abasi · September 19, 2011, 10:07

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.

September 14, 2011, 19:44	"du/dy" by "CEL" expression	#1
sajad_abasi Member sajad Join Date: Nov 2010 Posts: 51 Rep Power: 15	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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September 14, 2011, 23:25		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	u.Gradient y

September 18, 2011, 10:53		#3
sajad_abasi Member sajad Join Date: Nov 2010 Posts: 51 Rep Power: 15	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.

September 18, 2011, 18:24		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Can you explain what you are doing? Openings and outlets already set du/dy (normal to the interface) to zero.

September 19, 2011, 10:07		#5
sajad_abasi Member sajad Join Date: Nov 2010 Posts: 51 Rep Power: 15	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)landadu/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.