[fluid23]

That depends on the wall treatment you are using, the level of accuracy you want and many other factors. The ranges I gave are very broad and loose. If you want to be as accurate as possible use the near wall model and keep your y+ values as close to 1 as you can. Obviously, in most cases it would require cell by cell modification of the mesh to acheive that which you cannot do in star-ccm+. However, you should be able to keep it fairly constrained in a straight pipe like this.

I suggest you read up on the wall treatment methods to understand the specifics. The help docs have good discussions of each one.