# decrease in residual order and it's influence

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 July 19, 2002, 19:18 decrease in residual order and it's influence #1 michel Guest   Posts: n/a Hi, For the same test case (laminar flow over a flat plate) I'm using an explicit scheme and I'm facing an interesting event that I'm not able to understand. First as I set the CFL =0.5 at 3000 iterations I have 2 orders decrease in the residual. When I set the CFL= 0.3 I have 3 orders decrease in residual at 3000 iterations. However, the interesting point is that the solution seems much more converged at the higher CFL at 3000 iteration though the residual is 1 order higher that that of the CFL=0.3. What does the decrease in residual mean at this point??? I can't make sence of it?? If the decrease in residual measures the degree of convergence then theoretically the solution at the low CFL should look more converged.. Can anyone help? Thanks

 July 22, 2002, 08:38 Re: decrease in residual order and it's influence #2 Pete Guest   Posts: n/a You really need to compare the absolute magnitude of the residual as well. If you're just looking at order of magnitude reduction from the initial point, then this is dependent on the magnitude of the initial residual value. With a smaller CFL you will have a smaller residual and smaller changes in your solution. This may be what you're seeing.