wall shear stress

Todd

Dear all, I am writing a UDF to get the wss from fluent solver so that I can calculate the wss gradient and OSI. The problem is: I used this macro NV_V(wallshear, =, C_STORAGE_R_N3V(f,thread,SV_WALL_SHEAR)) to get the wall_shear_force, and then divided area.(wall_shear_force/area) to get the wss.

However, I found in the first/last 52 values is different from the values I got from fluent exported file. The magnitude of rest values are same but different direction(the value got from udf is positive while value from fluent is negative).

the mesh is 50X50X50 structured.

Does anyone know the reason?

Regards

Todd