Residuals do not decrease
 

Hi all,

I am simulating an unsteady flow. my problem is, in each time-step the residuals decrease very fast (like in 10 iterations) to 1e-4 but after that they keep decreasing very very slow to the desired residual criteria which is 1e-5 in my case. Most of the times, they will not reach this limit and simulation continues to next time-step when it reaches the maximum limit of iterations per time-step (which is 80 iterations in my case). Can anybody tell me where does this error come from?

is it from the grid or time step or anything else?