Wall Shear Stress prediction varies with fix y+
 

Dear all,

Let say I have a very simple rectangular duct. For flow development I develop the flow using 1000mm long channel and save the velocity profile xyz component and k-e at 80% of the duct. Recycle 4 times.

By measuring the wall shear stress, it shows that the shear stress is very consistent (straight line).

But when I imported to a shorter duct 70 mm (actual working duct)

with same input profile (xyz velocity, k -e).
The wall shear stress seems to be different. Why isn't it possible to maintain the same consistency. The y+ is the same. However, the cells in normal direction especially the cores varies for instances (50 cells, 40 cells, and 30 cells).

Could someone tell me if how wall shear stress achieve mesh independency? Is it possible to achieve absolute wall shear stress? just like the long duct.

Thanks

Regards,
Jee