# udf for wall slip

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 January 9, 2013, 06:39 udf for wall slip #1 New Member   ammm Join Date: Nov 2012 Posts: 20 Rep Power: 5 i need a udf for slip wall i want to use udf for setting this boundary condition: us=B*(du/dy) what should i do?

 January 10, 2013, 02:49 #2 Senior Member   SSL Join Date: Oct 2012 Posts: 227 Rep Power: 6 I have already written it. Email me please.

 January 10, 2013, 06:02 #3 New Member   ammm Join Date: Nov 2012 Posts: 20 Rep Power: 5 i emailed you thank you in advance

January 12, 2013, 13:58
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I also have written a UDF for slip velocity which works correctly, but when I want to add the term due to thermal creep, I get the below error:

I recognized that this error is due to using the expression "C_T_G(cell,t)" in my UDF.

Could you help me to solve this problem?

Thank you so much!

January 13, 2013, 00:26
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 Originally Posted by fahmadi Dear Mr Sadeghi I also have written a UDF for slip velocity which works correctly, but when I want to add the term due to thermal creep, I get the below error: "FLUENT received fatal signal (ACCESS_VIOLATION)." I recognized that this error is due to using the expression "C_T_G(cell,t)" in my UDF. Could you help me to solve this problem? Thank you so much!
In most Micro-Channel problems there is no need to add the thermal creep section. You can neglect it.

 January 15, 2013, 10:19 #6 New Member   ammm Join Date: Nov 2012 Posts: 20 Rep Power: 5 i write this udf for slip. is it correct??? #include "udf.h" DEFINE_PROFILE(shear_stressx, thread, n) { face_t f ; cell_t c0 ; Thread *t0 =THREAD_T0(thread) ; float u0,uw,vderivate, sstressx ; begin_f_loop(f, thread) { c0 = F_C0(f ,thread) ; vderivate= C_DUDY(c0,t0) ; u0 = C_U(c0, t0); uw=u0+1*pow(10,-6)*vderivate ; F_U(f, thread)=uw; sstressx = -.001003*vderivate ; F_PROFILE(f,thread,n) = sstressx ; } end_f_loop(f,thread)

 January 16, 2013, 05:49 How to write a slip condition in wall #7 New Member   Jetica Join Date: Jan 2013 Posts: 1 Rep Power: 0 dear Mr Sadeghi and ammm: i need a udf(fluent or cfx is ok) for slip wall.As ammm metioned,the slip wall which can be attached with thermal creep is the best.But if the thermal creep is excluded,that is ok. could you send me a udf you have writtern.please send the email:asm23374634@gmail.com thank you very much

 January 17, 2013, 06:03 #8 New Member   ammm Join Date: Nov 2012 Posts: 20 Rep Power: 5 my udf works good with low slip length but for larger slip length not converged. Can anyone guide me for this convergence problem? i use fluent 6.2 and when i dont use udf it works corrctly please help me

February 22, 2013, 17:10
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 Originally Posted by fahmadi Dear Mr Sadeghi I also have written a UDF for slip velocity which works correctly, but when I want to add the term due to thermal creep, I get the below error: "FLUENT received fatal signal (ACCESS_VIOLATION)." I recognized that this error is due to using the expression "C_T_G(cell,t)" in my UDF. Could you help me to solve this problem? Thank you so much!
I had same problem, to avoid this problem,you should not hook all your UDFs at the same time; Step by step! first apply the udf of slip velocity, then let the iterations go, after your solution is converged`,unhook it and apply Thermal creep udf, let it go for numerous iterations, then re-apply slip-velocity udf again,
All of these operations is due to suitable initializations which help Fluent to start a solution from a rather logic guess.
each UDF produces a sudden jump in the resodual graph, so it's better avoiding 3 jumps at the same time, instead, imply them gradually.

February 25, 2013, 05:32
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Quote:
 Originally Posted by ammm my udf works good with low slip length but for larger slip length not converged. Can anyone guide me for this convergence problem? i use fluent 6.2 and when i dont use udf it works corrctly please help me

Apply some under-relaxation.

Additionally, I can only emphasize once more that fluent comes with a BC of the type us=B*(du/dy).
It is called "Slip Boundary Formulation for Low-Pressure Gas System" and even includes the term for thermal creep.

 February 26, 2013, 00:44 #11 Senior Member   SSL Join Date: Oct 2012 Posts: 227 Rep Power: 6 I have done that before without thermal creep, but today have found how to consider thermal creep also. It needs step by step enabling and disabling equations.

 March 4, 2013, 06:34 #12 New Member   Katerina Join Date: Jul 2012 Posts: 2 Rep Power: 0 Dear all, I'm doing a simulation with slip and VOF. I would like to define slip - shear stress for liquid only. But I'm doing it wrong. My shear stress=mu*dudx*vof What should I change to get C_VOF for correct thread ? #include "udf.h" DEFINE_PROFILE(wall_shear_y,thread,position) { face_t f; Thread *t0, *t2, *t3; cell_t c0; double TAUxy, mu; double dudx; double vof; begin_f_loop(f,thread) { t0=THREAD_T0(thread); /*adjacent cell index*/ c0=F_C0(f,thread); /*adjacent cell thread*/ t2 = THREAD_SUB_THREAD(t0, 0); // take ID of phase no.1 t3 = THREAD_SUB_THREAD(t0, 1); // take ID of phase no.2 dudx=C_DUDX(c0,t0); mu=C_MU_L(c0,t0); /*viscosity*/ begin_c_loop(c0,t3) { vof=C_VOF(c0,t3); /*volume of fluid value in adjacent cell for phase 2*/ } end_c_loop(c0,t3) TAUxy=mu*dudx*vof; F_PROFILE(f,thread,position)=TAUxy; } end_f_loop(f,thread) } Regards, Katerina

 March 26, 2014, 05:41 slip wall shear #13 New Member   elaf Join Date: May 2013 Posts: 9 Rep Power: 5 I was wondering if any one can help me? I am using flow around rotating cylinder, the shear stresses at the wall need to be specified to constant value. In this option, there are 3 components for the shear stresses, i.e. x direction components and so on. Does anyone know for example how can set these values for cylinder surface Regard. Last edited by elaf_2003; March 26, 2014 at 13:52.

 November 13, 2014, 05:25 hi #14 Member   Qureshi M Z I Join Date: Sep 2013 Posts: 70 Rep Power: 4 hi, i need a UDF for slip boundary condition at the bottom of the domain or at the ground (wall), 3D case is just like a flow over a building. if anybody have sample UDF please share this, z is a vertical axis of my domain. thanks mziqureshi@hotmail.com regards,

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