valueFraction in partialSlip wall boundary condition

Saideep · January 31, 2018, 13:37

Hi everyone;

I am trying to use "partialSlip" boundary on a wall surface which requires the input variable named "valueFraction".

The "valueFraction" is bounded between 0 and 1 with 1 meaning no-Slip and 0 meaning slip. Intermediate value means, we have partial slip boundary condition.

I can see that the governing equation is of form: (1-valueFraction)*___. However, I am not able to fill the blank above.
I came across several posts on this topic but ultimately they were not answered at the end.

I feel the slip length, cell size and valueFraction are related in some way but not sure how.

Can anyone with experience help me in this regard?

Thanks.

Saideep · March 28, 2020, 10:16

Hi,

If anyone find it useful here it is:

$valueFraction = [\nabla]/[\nabla + 2 \lambda]$ where $[\nabla]$ = boundary cell size normal to the wall boundary and $[\lambda]$ is the user specified slip length.

Enjoy!!

yyq · June 14, 2020, 12:32

Hi, Saideep!

where do you know the expression of valueFraction? Or how could I derive it by myself.

Could you please explain it the issue?

Thanks.

pfavreau · June 23, 2020, 11:38

Quote:

Originally Posted by yyq

Hi, Saideep!

where do you know the expression of valueFraction? Or how could I derive it by myself.

Could you please explain it the issue?

Thanks.

Hi yyq,

I'm not sure but here is what I found about the expression of valueFraction provided by Saideep (see attached PDF). Tell me if it helps :-)

Saideep · June 24, 2020, 12:03

Hi,

Sorry for the late response.

Actually, there is a derivation to end up at this expression.

I remember years ago I found that on CFD online and copied to my notes. But now, my notes are preserved elsewhere and I cant find the thread precisely. I am sure it shall be on the forum.

Hope this helps.

yyq · June 25, 2020, 14:45

Quote:

Originally Posted by pfavreau

Hi yyq,

I'm not sure but here is what I found about the expression of valueFraction provided by Saideep (see attached PDF). Tell me if it helps :-)

Hi pfavreau,

thanks for your answer, it really helps a lot.

yyq · June 25, 2020, 14:46

Hi Saideep,

thanks anyway!!

damu1414 · January 26, 2021, 12:31

Hello everyone,

Thanks for the discussion. I need to use partialSlip for my simulations. Can any body say if slip length has any relationship with mean free path in Knudsen number?

Thank you

January 31, 2018, 13:37	valueFraction in partialSlip wall boundary condition	#1
Saideep Senior Member Saideep Join Date: Apr 2015 Location: INDIA Posts: 203 Rep Power: 12	Hi everyone; I am trying to use "partialSlip" boundary on a wall surface which requires the input variable named "valueFraction". The "valueFraction" is bounded between 0 and 1 with 1 meaning no-Slip and 0 meaning slip. Intermediate value means, we have partial slip boundary condition. I can see that the governing equation is of form: (1-valueFraction)___. However, I am not able to fill the blank above. I came across several posts on this topic but ultimately they were not answered at the end. I feel the slip length, cell size and valueFraction* are related in some way but not sure how. Can anyone with experience help me in this regard? Thanks. mojijoon and Znoel_7520 like this.

March 28, 2020, 10:16		#2
Saideep Senior Member Saideep Join Date: Apr 2015 Location: INDIA Posts: 203 Rep Power: 12	Hi, If anyone find it useful here it is: $valueFraction = [\nabla]/[\nabla + 2 \lambda]$ where $[\nabla]$ = boundary cell size normal to the wall boundary and $[\lambda]$ is the user specified slip length. Enjoy!! PositronCascade likes this.

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June 14, 2020, 12:32		#3
yyq New Member Yuqiang Yao Join Date: Jun 2020 Posts: 3 Rep Power: 6	Hi, Saideep! where do you know the expression of valueFraction? Or how could I derive it by myself. Could you please explain it the issue? Thanks.

June 24, 2020, 12:03		#5
Saideep Senior Member Saideep Join Date: Apr 2015 Location: INDIA Posts: 203 Rep Power: 12	Hi, Sorry for the late response. Actually, there is a derivation to end up at this expression. I remember years ago I found that on CFD online and copied to my notes. But now, my notes are preserved elsewhere and I cant find the thread precisely. I am sure it shall be on the forum. Hope this helps.

June 25, 2020, 14:46		#7
yyq New Member Yuqiang Yao Join Date: Jun 2020 Posts: 3 Rep Power: 6	Hi Saideep, thanks anyway!!

January 26, 2021, 12:31		#8
damu1414 New Member damu Join Date: Feb 2017 Posts: 24 Rep Power: 9	Hello everyone, Thanks for the discussion. I need to use partialSlip for my simulations. Can any body say if slip length has any relationship with mean free path in Knudsen number? Thank you