Hi,

I need to get wall shear strees values by writing UDF. I found out a discussion about this topic in this forum between Mike and Markus, but it did not help me. So, is there any macro to find wall shear stress?

I was also thinking about getting this values in an different way. Fluent can give the values as a postprocess.So, can I save the values in a file and then read in my UDF? I think, the DEFINE_RW_FILE (Section 4.2.5) macro can do this, but i don't know how to do? Could you please give some detailed advices?

Best Regards...

Melih

Doesn't Fluent allow for the solution of wall shear stresses already? I don't think you need a UDF.

include storage.h header file

define real wallshear[ND_ND];

face = face variable ;

tf= face thread

NV_V (wallshear, =, C_STORAGE_R_NV(face,tf,SV_WALL_SHEAR));

this will give you the wall_shear_force multiplying by the area vector would give you the wall_shear_stress.

Hope this helps ,

Ajay

Thanks Ajay, I'll work on it...

Hi Ajax,

I used the macro given by you. The macro seems to give the wall_shear_force as you said.I got these forces as wallshear[0],wallshear[1] and wallshear[2]. In order to get the stress, I divided these components by the magnitude of face area normal which is simply the area of each face. After doing this, I assumed that I got the stresses in x,y and z direction. But the problem is that, although the order of magnitude are resonable by the wall shear stress found by FLUENT, they are not equal(sometimes I get negative and positive values, but FLUENT gives positive, and vice versa) . However,when I calculated the magnitude of wall shear, I saw that they were nearly equal with that of FLUENT. Any comments?