[zxj160]

I define the inlet and outlet as cyclic BC. But now I want to set the outlet as convective BC for the passive scalar. Is it possible to achieve that?

[zxj160]

Or how to define other types of BC for cyclic patches? such as zeroGradient?

Does any one have the experience of creating this kind of customer cyclic derived BC?

[chegdan]

Originally Posted by zxj160

Or how to define other types of BC for cyclic patches? such as zeroGradient?

Does any one have the experience of creating this kind of customer cyclic derived BC?

The way I got around this easily was to use directMapped for momentum (setting it to an average velocity or flowrate) and that allows you to use fixed and zeroGradient boundary conditions for your passive scalar.

Dan

[zxj160]

Originally Posted by chegdan

The way I got around this easily was to use directMapped for momentum (setting it to an average velocity or flowrate) and that allows you to use fixed and zeroGradient boundary conditions for your passive scalar.

Dan

Dear Dan,

Thanks. Do you mean that I set inlet and outlet as normal 'patch' type and use directMapped to map the cyclic velocity? Then I can set uniform value and zeroGradient for passive scalar?

If yes, I have tried this and also mapped pressure. But the output of pressure is so different (all the other conditions are same)?

for cyclic case:
p
(
0.000572052
0.000389558
6.02371e-05
-0.000262527
-0.000663079
-0.00121091
-0.00193648
-0.00261434
.......

for directMapped case:
p
(
126.072
126.067
126.061
126.055
126.052
126.049
.......

I can not identify the problem.

[chegdan]

Originally Posted by zxj160

Dear Dan,

Thanks. Do you mean that I set inlet and outlet as normal 'patch' type and use directMapped to map the cyclic velocity? Then I can set uniform value and zeroGradient for passive scalar?

If yes, I have tried this and also mapped pressure. But the output of pressure is so different (all the other conditions are same)?

for cyclic case:
p
(
0.000572052
0.000389558
6.02371e-05
-0.000262527
-0.000663079
-0.00121091
-0.00193648
-0.00261434
.......

for directMapped case:
p
(
126.072
126.067
126.061
126.055
126.052
126.049
.......

I can not identify the problem.

Is your pressure drop through the domain the same? I always never use directMapped for pressure. The values will be different than the cyclic case since its pressure driven in the directMapped case.

[zxj160]

Originally Posted by chegdan

Is your pressure drop through the domain the same? I always never use directMapped for pressure. The values will be different than the cyclic case since its pressure driven in the directMapped case.

Yes, the pressure drop is same and only the BCs for pressure are different. But the pressure is also cyclic. If we do not use cyclic, then what type of BC can we define for pressure.

Best regards,
Jian

[chegdan]

Originally Posted by zxj160

Yes, the pressure drop is same and only the BCs for pressure are different. But the pressure is also cyclic. If we do not use cyclic, then what type of BC can we define for pressure.

Best regards,
Jian

0 on the outlet and zeroGradient on the inlet.

See tutorials/incompressible/pisoFoam/les/pitzDailyDirectMapped for inspiration

[zxj160]

Originally Posted by chegdan

0 on the outlet and zeroGradient on the inlet.

See tutorials/incompressible/pisoFoam/les/pitzDailyDirectMapped for inspiration

Many thanks. I will try it later. By the way, is there any tutorials introducing pressure (p) in the OpenFOAM? Because I cannot understand the meaning of pressure clearly?

[april0100]

Pressure is typically normalized by density in OpenFOAM, hence the units [m^2/s^2].

[cfdonline2mohsen]

This is true only for incompressible flow, but for the compressible flow the dimension of pressure is
dimensions [1 -1 -2 0 0 0 0];
check the 0 folder of incompressible & compressible cases in Tutorial