In udf I used:

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

to get the wall shear. But the results seems a mess. I tested in a simple channel flow. Some point the wall shear is negative, some is positive. It is not right at all. But when I use XY plot, it seems right. I am not sure if the udf macro I used fetched the right variable. Do you know how the get the wall shear? Thanks!

Yes, the macro indeed gives you the wall shear force vector ( it has 3 components ) .

-Ajay