STEM

Two phase simulation

• Chinmaya Kumar Patra
Subscriber

I am trying to do a two-phase boiling simulation in fluent in a rectangular channel. I have given constant mass flux inlet as inlet BC and gauge zero pressure as the outlet BC. For outlet BC for vapor, its showing two options neighboring cell or back volume fraction as 0, which one out of these two i should select for simulation or please tell on what basis we should choose out of these two?

• Rob
Ansys Employee

Backflow is what you get when something enters the domain from the outlet. Ideally this shouldn't happen, but the option is there in case it does. The settings want to be as close to what's leaving the domain as possible. Neighbouring cell is good for flow direction, otherwise it's normal to the facet.

• Chinmaya Kumar Patra
Subscriber

In may case for each time step i have mentioned max 20 iteration and neighbouring cell  as volume fraction fpecification method, but while solving for time steps its shwoing "Reversed flow on 19 faces of pressure-outlet 5" message for each iteration, and at the end "solution is converged", what does it mean? I have attached a text file with two time step for your reference with the above mentioed messages.

Flow time = 0.02499868241670707s, time step = 20643

Global Courant Number [Variable Time Step Criteria] : 0.441283

Updating solution at time level N...

Global Courant Number [Explicit VOF Criteria] : 0.153555
done.
physical-dt  1.0000e-06

iter  continuity  x-velocity  y-velocity  z-velocity      energy     time/iter
370599  7.6244e-05  6.7564e-09  6.6296e-09  9.4738e-09  1.8337e-11  0:00:00   20

Reversed flow on 19 faces of pressure-outlet 5.
370600  2.3498e-01  1.2303e-05  1.1941e-05  1.3743e-05  3.6681e-05  0:00:01   19

Reversed flow on 19 faces of pressure-outlet 5.
370601  2.7168e-02  5.7825e-06  5.7242e-06  6.5056e-06  6.2679e-07  0:00:00   18

Reversed flow on 19 faces of pressure-outlet 5.
370602  1.7321e-02  1.6978e-06  1.6518e-06  1.8528e-06  8.3496e-08  0:00:00   17

Reversed flow on 19 faces of pressure-outlet 5.
370603  1.2406e-02  8.9093e-07  8.9053e-07  1.0275e-06  2.3910e-08  0:00:00   16

Reversed flow on 19 faces of pressure-outlet 5.
370604  9.0921e-03  7.4967e-07  7.6008e-07  8.8222e-07  7.6721e-09  0:00:00   15

Reversed flow on 19 faces of pressure-outlet 5.
370605  6.6246e-03  6.3146e-07  6.3900e-07  7.4103e-07  2.7183e-09  0:00:00   14

Reversed flow on 19 faces of pressure-outlet 5.
370606  4.7882e-03  5.0056e-07  5.0368e-07  5.8592e-07  1.1237e-09  0:00:00   13

Reversed flow on 19 faces of pressure-outlet 5.
370607  3.4446e-03  3.8009e-07  3.8047e-07  4.4329e-07  5.6069e-10  0:00:00   12

Reversed flow on 19 faces of pressure-outlet 5.
370608  2.4715e-03  2.8101e-07  2.8003e-07  3.2685e-07  3.2886e-10  0:00:00   11

Reversed flow on 19 faces of pressure-outlet 5.
370609  1.7704e-03  2.0421e-07  2.0288e-07  2.3757e-07  2.1352e-10  0:00:00   10

Reversed flow on 19 faces of pressure-outlet 5.

iter  continuity  x-velocity  y-velocity  z-velocity      energy     time/iter
370610  1.2677e-03  1.4680e-07  1.4557e-07  1.7131e-07  1.4667e-10  0:00:00    9

Reversed flow on 19 faces of pressure-outlet 5.
370611  9.0807e-04  1.0479e-07  1.0380e-07  1.2298e-07  1.0215e-10  0:00:00    8

Reversed flow on 19 faces of pressure-outlet 5.
370612  6.5202e-04  7.4474e-08  7.3717e-08  8.8076e-08  7.2170e-11  0:00:00    7

Reversed flow on 19 faces of pressure-outlet 5.
370613  4.6888e-04  5.2779e-08  5.2212e-08  6.3012e-08  5.0949e-11  0:00:00    6

Reversed flow on 19 faces of pressure-outlet 5.
370614  3.3765e-04  3.7336e-08  3.6917e-08  4.5067e-08  3.6300e-11  0:00:00    5

Reversed flow on 19 faces of pressure-outlet 5.
370615  2.4338e-04  2.6383e-08  2.6072e-08  3.2238e-08  2.6007e-11  0:00:00    4

Reversed flow on 19 faces of pressure-outlet 5.
370616  1.7570e-04  1.8632e-08  1.8400e-08  2.3076e-08  1.8769e-11  0:00:00    3

Reversed flow on 19 faces of pressure-outlet 5.
370617  1.2695e-04  1.3154e-08  1.2980e-08  1.6535e-08  1.3627e-11  0:00:00    2

Reversed flow on 19 faces of pressure-outlet 5.
370618  9.1844e-05  9.2854e-09  9.1540e-09  1.1867e-08  9.9896e-12  0:00:00    1
!370618 solution is converged
Flow time = 0.02499968241670707s, time step = 20644

Global Courant Number [Variable Time Step Criteria] : 0.145451

Updating solution at time level N...

Global Courant Number [Explicit VOF Criteria] : 0.0483624
done.
physical-dt  3.1758e-07

iter  continuity  x-velocity  y-velocity  z-velocity      energy     time/iter
370618  9.1844e-05  9.2854e-09  9.1540e-09  1.1867e-08  9.9896e-12  0:00:00   20

Reversed flow on 19 faces of pressure-outlet 5.
370619  3.2095e-02  4.0304e-06  3.9061e-06  4.5219e-06  1.1961e-05  0:00:00   19

Reversed flow on 19 faces of pressure-outlet 5.
370620  8.1917e-03  3.4091e-06  3.4359e-06  3.6267e-06  7.1104e-08  0:00:00   18

Reversed flow on 19 faces of pressure-outlet 5.
370621  6.3102e-03  3.4113e-06  3.4373e-06  3.6405e-06  7.0692e-09  0:00:00   17

Reversed flow on 19 faces of pressure-outlet 5.
370622  4.8154e-03  2.9165e-06  2.9366e-06  3.1148e-06  1.8227e-09  0:00:00   16

Reversed flow on 19 faces of pressure-outlet 5.
370623  3.6150e-03  2.2834e-06  2.2971e-06  2.4394e-06  5.4397e-10  0:00:00   15

Reversed flow on 19 faces of pressure-outlet 5.
370624  2.6823e-03  1.7079e-06  1.7169e-06  1.8239e-06  1.9852e-10  0:00:00   14

Reversed flow on 19 faces of pressure-outlet 5.
370625  1.9749e-03  1.2454e-06  1.2511e-06  1.3294e-06  1.0016e-10  0:00:00   13

Reversed flow on 19 faces of pressure-outlet 5.
370626  1.4469e-03  8.9475e-07  8.9831e-07  9.5482e-07  6.4478e-11  0:00:00   12

Reversed flow on 19 faces of pressure-outlet 5.
370627  1.0573e-03  6.3702e-07  6.3922e-07  6.7990e-07  4.4939e-11  0:00:00   11

Reversed flow on 19 faces of pressure-outlet 5.
370628  7.7122e-04  4.5096e-07  4.5231e-07  4.8161e-07  3.1496e-11  0:00:00   10

Reversed flow on 19 faces of pressure-outlet 5.

iter  continuity  x-velocity  y-velocity  z-velocity      energy     time/iter
370629  5.6189e-04  3.1810e-07  3.1891e-07  3.4002e-07  2.2032e-11  0:00:00    9

Reversed flow on 19 faces of pressure-outlet 5.
370630  4.0911e-04  2.2386e-07  2.2433e-07  2.3955e-07  1.5472e-11  0:00:00    8

Reversed flow on 19 faces of pressure-outlet 5.
370631  2.9767e-04  1.5729e-07  1.5756e-07  1.6852e-07  1.0914e-11  0:00:00    7

Reversed flow on 19 faces of pressure-outlet 5.
370632  2.1699e-04  1.1041e-07  1.1055e-07  1.1845e-07  7.7326e-12  0:00:00    6

Reversed flow on 19 faces of pressure-outlet 5.
370633  1.5822e-04  7.7444e-08  7.7516e-08  8.3213e-08  5.5071e-12  0:00:00    5

Reversed flow on 19 faces of pressure-outlet 5.
370634  1.1547e-04  5.4297e-08  5.4326e-08  5.8435e-08  3.9415e-12  0:00:00    4

Reversed flow on 19 faces of pressure-outlet 5.
370635  8.4327e-05  3.8056e-08  3.8061e-08  4.1026e-08  2.8273e-12  0:00:00    3
!370635 solution is converged
Flow time = 0.025s, time step = 20645
Specified flow time reached    flow time = 0.025, total time = 0.025

• Rob
Ansys Employee

It means the time step has converged and you have flow into the domain from the outlet.

• Chinmaya Kumar Patra
Subscriber

Yes, for all time step i have converged solution but what does 19 faces of pressure-outlet 5 mean? if you can clrify it will help