[steampunc]

Thanks in advance for the potential help. I'm relatively new to OpenFoam, so I'm really sorry if this is a stupid mistake. I can't seem to find the same problem online, but I've been searching for a couple days.

I've been trying to apply some diagnostic/validation tests to incompressible pimpleFoam configurations and have been finding some anomalous results.

For any incompressible fluid, div(U) should be 0 or very near it. From what I understand, the pimpleFoam solver uses the div(U) -> 0 condition as it solves the pressure field, and it certainly seems to be doing that, because in each step the time continuity errors are very small (order 10^-17 or so). However, when I use funkySetFields/postProcess to compute the div(U) field at a given logged time, the values are much larger (on order 1 or even larger). I've tried it on my own configurations, along with several of the pimpleFoam/pisoFoam tutorials, and all of them result in large div(U) fields.

To compute the field, I've been using these commands:

 funkySetFields -time 0: -create -field divU -expression "div(U)"

and

postProcess -func "div(U)"

From what I understand, postProcessing (and funkySetFields?) uses the same divergence schemes as OpenFoam itself, so I'm confused why it's so large. I'm almost completely certain it's due to user error, but it seems like such a simple test that there's not much room for it to go wrong.

I've been using a Gaussian divergence scheme with linear interpolation in system/fvSchemes for div(U).

Attached are some images of the div(U) field in different pimpleFoam tutorial cases in paraView.









Also, here are some excerpts of logs from the pimpleFoam runner on channel395:

PIMPLE: iteration 1
smoothSolver:  Solving for Ux, Initial residual = 0.0117778, Final residual = 5.81593e-06, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.0603226, Final residual = 2.72548e-06, No Iterations 3
smoothSolver:  Solving for Uz, Initial residual = 0.0585004, Final residual = 2.7339e-06, No Iterations 3
Pressure gradient source: uncorrected Ubar = 0.1335, pressure gradient = 2.76228e-05
GAMG:  Solving for p, Initial residual = 0.146204, Final residual = 0.0126411, No Iterations 1
time step continuity errors : sum local = 1.14563e-05, global = -8.27789e-20, cumulative = -2.0927e-18
Pressure gradient source: uncorrected Ubar = 0.1335, pressure gradient = 2.76872e-05
GAMG:  Solving for p, Initial residual = 0.0163918, Final residual = 4.2532e-07, No Iterations 5
time step continuity errors : sum local = 4.5834e-10, global = -1.12784e-19, cumulative = -2.20548e-18
Pressure gradient source: uncorrected Ubar = 0.1335, pressure gradient = 2.76392e-05
ExecutionTime = 14.27 s  ClockTime = 14 s

fieldAverage fieldAverage1 write:
    Calculating averages

Courant Number mean: 0.30284 max: 0.540451
Time = 5.4

PIMPLE: iteration 1
smoothSolver:  Solving for Ux, Initial residual = 0.0118056, Final residual = 5.80108e-06, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.0603712, Final residual = 2.65463e-06, No Iterations 3
smoothSolver:  Solving for Uz, Initial residual = 0.0584964, Final residual = 2.67235e-06, No Iterations 3
Pressure gradient source: uncorrected Ubar = 0.1335, pressure gradient = 2.76884e-05
GAMG:  Solving for p, Initial residual = 0.146366, Final residual = 0.0127159, No Iterations 1
time step continuity errors : sum local = 1.15734e-05, global = -1.22909e-19, cumulative = -2.32839e-18
Pressure gradient source: uncorrected Ubar = 0.1335, pressure gradient = 2.77468e-05
GAMG:  Solving for p, Initial residual = 0.0165409, Final residual = 5.45694e-07, No Iterations 5
time step continuity errors : sum local = 5.65104e-10, global = -1.5652e-20, cumulative = -2.34404e-18
Pressure gradient source: uncorrected Ubar = 0.1335, pressure gradient = 2.76982e-05
ExecutionTime = 14.61 s  ClockTime = 15 s

fieldAverage fieldAverage1 write:
    Calculating averages

Courant Number mean: 0.302862 max: 0.539102
Time = 5.6