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UDS problem with wall boundary condition

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Old   November 12, 2005, 12:14
Default UDS problem with wall boundary condition
  #1
Alex F.
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As we know, face values of quantities in FLUENT are allocated in memory only for boundary faces (e.g., wall zones).

I wrote a UDF which adds a UDS equation to the system of equations. I have a problem with WALL boundary condition.

The problem is that FLUENT does not have access to face values of WALL boundary condition (e.g., F_R, F_U) and when calling these face values ACCESS_VIOLATION occured.

I did not see this problem for other kinds of boundary condition like OUTFLOW, VELOCITY INLET.

Thanks in advance.
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Old   November 13, 2005, 05:02
Default Re: UDS problem with wall boundary condition
  #2
RoM
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F_U should be zero at walls (no slip) if not statet otherwise. Other face values can be calculated from cell gradient and vector cell_center->face_center (dr0). For density: face_density=NV_DOT(C_R_G(c0,t0),dr0).

RoM
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Old   November 13, 2005, 06:52
Default Re: UDS problem with wall boundary condition
  #3
Alex F.
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Dear RoM, Thanks for your prompt response.

FLUENT should automatically return F_U=0 at WALL boundary. But when F_U is called in the UDF for WALL boundary, ACCESS_VIOLATION occured.

There is a sample for DEFINE_UDS_FLUX in UDF manual in which F_R, F_U and F_V has been used. But when these functions want to return the value of WALL boundary ACCESS_VIOLATION occured.
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Old   November 13, 2005, 10:03
Default Re: UDS problem with wall boundary condition
  #4
KP
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Is there by any chance u want to code for wall force?? KP
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Old   November 13, 2005, 14:28
Default Re: UDS problem with wall boundary condition
  #5
Alex F.
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No, I want to calculate flux through wall. I used a face loop:

thread_loop_f(t,d) {

begin_f_loop(f,t)

{

flux=F_R(f,t)*F_U(f,t);

}end_f_loop(f,t) }

this will cause ACCESS_VIOLATION when "f" belongs to WALL boundary. Other type of boundary such as "Inlet", "Outflow" does not cause ACCESS_VIOLATION.
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Old   November 14, 2005, 02:41
Default Re: UDS problem with wall boundary condition
  #6
RoM
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You can use the F_FLUX(f,t) macro for that purpose.

RoM
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Old   November 14, 2005, 04:26
Default Re: UDS problem with wall boundary condition
  #7
Luca
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Dear Alex, the problem is that F_ macros, works only with the segregated solver.Luca
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Old   November 14, 2005, 04:30
Default Re: UDS problem with wall boundary condition
  #8
RoM
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F_R(f,t) crashes on segeregated solver when used on walls. I tried it.

RoM
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Old   November 14, 2005, 04:40
Default Re: UDS problem with wall boundary condition
  #9
Luca
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Yes I had the same problem. In the fluent users guide, it's written clearly that F_ are only for the segregated. So if you use the coupled 2nd order you can use the gradient to build wall variables. Luca
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Old   November 14, 2005, 05:11
Default Re: UDS problem with wall boundary condition
  #10
RoM
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@Luca, Do you have some experience with calculation of face data from cell data? I had some problems with it and started a thread one week ago, but nobody had an answer. Maybe you can help. Thats what i wrote:

I have got a problem with the calculation of face vaules from cell center values. For an interior face i could caculate the face value either from the c0 cell side or the c1 cell side, using the cell values and the gradient. For a species it looks like this

from c0

face_value0=C_YI(c0,c0thread,i)+NV_DOT(C_YI_G(c0,c 0thread,i),dr0)

and from c1

face_value1=C_YI(c1,c1thread,i)+NV_DOT(C_YI_G(c1,c 1thread,i),dr1)

dr is the vector from cell center to the face center. Both face values should be identical but unfortunatly they are not. I tried it on a sturcured meshe with full converged soultion. Is there any other way to get consistent values for the faces?

Thanks for any suggestions

RoM

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Old   November 14, 2005, 06:16
Default Re: UDS problem with wall boundary condition
  #11
Luca
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Dear RoM, I used only c0 to build wall pressure, so I haven't tested my routine on interior faces. Sorry. I hope the difference you found is not so large beetween using c0 or c1.It should depend on the gradient. Try using node based gradient and let me know how it works. Luca
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Old   November 14, 2005, 06:23
Default Re: UDS problem with wall boundary condition
  #12
RoM
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I will give it try. Thanks for the suggestion. The manual stated one should use reconstruction gradients (RG) to build face values from cell values but i never got this to work. Everytime i try to access a RG fluent gives a nice access violation. I wonder if RG are available at all.

RoM
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Old   November 14, 2005, 06:31
Default Re: UDS problem with wall boundary condition
  #13
Luca
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I found out that sometimes instead of using reconstructed gradient, you should use the default one. It depends on the solver you're using (segregated or coupled).Luca
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Old   November 14, 2005, 06:39
Default Re: UDS problem with wall boundary condition
  #14
RoM
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I only use the segragated solver so i think i am stuck with the default gradients.

Thanks, RoM
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Old   August 6, 2014, 05:08
Default Reconstruction Gradient
  #15
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hanSolo
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User89 is on a distinguished road
Hi, did you find a way to store cell values at faces by using the reconstruction Gradient?

Thanks a lot
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