problems with 90 elbow and make sure y+<1
 

Hi all,
I use ICEM to get structure hexa mesh. Here is how I block the elbow.(due to y+<1, the first layer is less than 0.00085mm)
https://imgly.net/img/3LT.md.png
But when I set nodes number either more than 33 or less than 33 in the Circumferential direction, there will exist negative volume
https://imgly.net/img/3L8.md.png
By the way, the contours of y+ is also strange(this time I use more block at the elbow part)
https://imgly.net/img/3LR.md.png
this is the cell mass fraction of first layer, and is seems to be wrong.
https://imgly.net/img/3LI.md.png
so anyone can help me?
Thanks.