Grid Independency modeling - Grading meshes
 

Hi,
I am working on turbulent pipe flows(2D Model in GAMBIT and Fluent 2d-Axisymmetric Analysis). Well, I need help regarding the inputs for grading meshes. For example the three mesh sizes, I am working on the same pipe, be 400x20, 800x40, 1600x80 (Fundamental exercises).
Now after analyzing the models (non graded mesh or uniform mesh), I see that the results are NOT GRID INDEPENDENT. Hence I started working on non uniform (graded) meshes for these mesh sizes. Well, for the First/Last Ratio type of grading,

Ratio = (last length/first length)^(1/n-1).
where n= no: of intervals on the edge

Now my Questions are
1) "Are we supposed to give same ratio to different mesh sizes i.e say 0.5 for both 800 intervals edge and 1600 intervals edge (or) are we supposed to provide separate ratios for checking GRID INDEPENDENCY?"

2) "How to consider/decide the value of last elemental length or first elemental length for a given edge so as to use those values in above formula to get the ratio?"

:) Thank you for your help :)