udf for wall slip
 

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?

I have already written it. Email me please.

i emailed you thank you in advance

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.

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)

How to write a slip condition in wall
 

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

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:(

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.

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.

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.

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

slip wall shear
 

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.

hi
 

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,

UDF Slip Rotational Wall
 

Hi,
i need the udf for slip rotational wall. in this case i want to simulate for 2-d journal bearing. what should i do?
Thanks.

Dear msaeedsadeghi
Hi I'm doing about micro-channel problem. so I need the udf(fluent) for slip condition for slip wall.
if you have udf of slip condition and temperature jump condition.
Could you send me the udf code? It doesn't matter if it not include thermal creep
my email : ssdssdblack@naver.com
thank you

Can you send me the udf file for us=b*(du/dy) model .
Email :syedumer46@gmail.com

Would you please mail me the udf, thanks a lot! My e_mail is 4963404@qq.com

I hope anybody reading this is aware that low pressure boundary slip is for a long time already included in Fluent, without needing to add any UDFs. Look for "low pressure boundary slip" in the manual to find out more.

Dear Mr. Sadeghi

Can you mail me the UDF? I, require this UDF for a simulation of flow through a micro-channel. My e-mail is - bishaktomanush@gmail.com

regards
S. G. Das