Onera Wing Wall function?

Dianhong

Dear friends,

I am walking through Onera Wing problemat http://www.grc.nasa.gov/WWW/wind/val.../m6wing01.html

From the case description, it says: " However, the spacing of the grid normal to the wing surface is approximately 5.0E-05 feet, which will only resolve the turbulent boundary layer with the first grid point off the wall of y+ of approximately 30. Thus, the wall function will be used with this grid. ".

Here are my questions: 1). What is the wall function mentioned above? What is the purpose of it? 2). What is the definition of y+ here, since I can not get the y+=30 from above?

Many thanks!