[calf.Z]

hello everyone,
I am doing DNS on gas flow in heated pipe. The residuals keep horizontal when running, but the order of magnitude of residual is not low enough. And I check the average temperature on wall, it doesn't reach the expected result, which means the case has not get converged. I changed the settings of fvscheme and fvsolution, but it has no influence on residuals.

I am wondering the reason that may cause the horizontal residual and how I can solve this situation. Thank you.