CFD++ Residual plot and convergence problem
 

Hello,
I am new in the website, and would really appreciate all of your help.

I have a basic 2D mesh and I am trying to do a grid convergence study. It is a study of hypersonic flow with a lot of reactions and plasma flow (re-entry). I used ICEM to generate the mesh and then used CFD++. Although my first mesh(which was coarser) converged and the residuals dropped until nearly e-4, when I decreased the cell sizes a little bit and made some little corrections on the parameters of exponential1 on an edge in ICEM, I obtained a residual plot which dropped only until between e-1 and e-2 (residual plot is also attached).
I ran the program until 5000 steps but there was no use.

What can be the reason?
Should a residual plot drop until e-10 orders?
Can I use my results, are they correct with a residual like that?
What really does the residual plot mean?

Thanks in advance :)
Emre