[sgalway]

Is there a disadvantage to a small Y+? I know for shear stress transport models I am looking for a Y+ less than approximately 2. Is there a disadvantage/error to having this number much smaller than that (like 0.2 for example)?

[aatman]

Originally Posted by sgalway

Is there a disadvantage to a small Y+? I know for shear stress transport models I am looking for a Y+ less than approximately 2. Is there a disadvantage/error to having this number much smaller than that (like 0.2 for example)?

Are you simulating a wall-bounded turbulent flow? if you use DNS or LES your first computational node off the wall must be at y1+ = 1 or even y1+=0.5, but this mean a very large ammount of nodes. With wall function (this means that you are not making DNS anymore) you can put your first node in the log zone, so y1+ > 30, and you can save the number of computational nodes.

[cfd_lean]

Hi For wall integration grids we need to have y plus around 0.2 to 1. where as with the low y plus values you will see some convergence issues. With the low y plus values there is possibility to predict wrong gradients. That will screw up your complete solution.

[sgalway]

Originally Posted by aatman

Are you simulating a wall-bounded turbulent flow? if you use DNS or LES your first computational node off the wall must be at y1+ = 1 or even y1+=0.5, but this mean a very large ammount of nodes. With wall function (this means that you are not making DNS anymore) you can put your first node in the log zone, so y1+ > 30, and you can save the number of computational nodes.

I am modeling the leg of an offshore jackup drilling rig. Therefore, this is an open flow around an obstruction.

Originally Posted by cfd_lean

Hi For wall integration grids we need to have y plus around 0.2 to 1. where as with the low y plus values you will see some convergence issues. With the low y plus values there is possibility to predict wrong gradients. That will screw up your complete solution.

Can you expand on the "convergence issues". Why would low Y+ values give convergence problems?

Thanks for all the help. I really appreciate it.