[ripperjack]

Hi all,

I am simulating DNS channel flows based on the buoyantBuosinesqPimpleFoam. I found that if I set the the p tolerance=1e-6 in system/fvSolution, the calculation is very slow and the problem is that the iteration No. for p is very large (more than 200 iterations!), which can be seen as follow. My time step is 0.001.
I want to speed up the simulation. One possible way is to decrease the p tolerance to 1e-5. But I want to know, if I do this, how can I ensure the continuity? I have no idea what time step continuity errors means, I check the source codes and it seems that this error also include time step value and there are sum local, global, and cumulative errors, which one is more important?? Anyway, my question is: how much of the continuity error is acceptable for a DNS simulation? Many thanks, guys!

Courant Number mean: 0.288069 max: 0.61355
DILUPBiCG:  Solving for Ux, Initial residual = 0.00630291, Final residual = 1.07118e-07, No Iterations 3
DILUPBiCG:  Solving for Uy, Initial residual = 0.0432376, Final residual = 6.85184e-07, No Iterations 3
DILUPBiCG:  Solving for Uz, Initial residual = 0.0399243, Final residual = 6.44705e-07, No Iterations 3
DILUPBiCG:  Solving for rho, Initial residual = 0.0135317, Final residual = 2.42912e-07, No Iterations 3
DICPCG:  Solving for p_rgh, Initial residual = 0.791976, Final residual = 4.79033e-05, No Iterations 79
time step continuity errors : sum local = 2.55569e-08, global = 5.12662e-20, cumulative = 1.1254e-19
DICPCG:  Solving for p_rgh, Initial residual = 0.0616171, Final residual = 9.11894e-07, No Iterations 219
time step continuity errors : sum local = 3.40954e-10, global = 5.92299e-20, cumulative = 1.7177e-19