[ndabir]

Hi All,

I have a rather simple though important question. I am doing an unsteady analysis of a compressible flow using coupled pressure-based solver (The reason I use pressure-base is I have to use VOF method which is not compatible with density-base solver).

My main question is how can I do a reliable mesh size and time step size independence study so that I can make sure my results will not change further significantly? Here is what I think:

1) Shall I first fix time step and refine grid. Then when the results are almost independent, refine the time step on that grid to find the desired time step?

2) Or shall I use a fix CFL number for the flow (such as 0.25), and based on CFL= velocity of sound*dt/dx and a grid size (dx), find the time step and do a simulation. Then by keeping CFL the same (0.25), half the grid size (therefore the time step should be half) and do another simulation and compare the results?

Is there another method too?
Are both the 1st and 2nd methods I mentioned above correct?