CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

Outlet temperature too low, bc problem

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 10, 2020, 20:22
Default Outlet temperature too low, bc problem
  #1
Member
 
Alex
Join Date: May 2019
Posts: 35
Rep Power: 3
Sedullo is on a distinguished road
Hello to everyone, I am simulating a natural convection problem, where only the wavy part of the right side wall is heated, the heated air is flowing upward. The temperature of the air entering the channel is set to 300 K and the temperature of the heated wall to 340 K.

I do not understand why the temperature at the outlet is so low, as you can see in the pictures attached. In the second picture the velocity vectors are shown.

I guess the problem is in the bc. Here I copy the bc of the velocity and the temperature.
Code:
dimensions      [0 0 0 1 0 0 0];

internalField   uniform 300;

boundaryField
{
    sideWallheated
    {
        type            fixedValue;
        value           uniform 340;
    }
    
    sideWallsNotheated
    {
        type            zeroGradient;
    }

    inlet
    {
        type            inletOutlet;
        inletValue      uniform 300;
        value           uniform 0;
    }

    outlet
    { 
        type            outletInlet;
        outletValue     uniform 300;
        value           uniform 0;
    }


Code:
dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    sideWallheated
    {
        type            noSlip;
    }

    sideWallsNotheated
    {
        type            slip;
    }

    inlet
    {
        type            outletInlet;
        outletValue     uniform (0 0 0);
        value           uniform (0 0 0);
    }


    outlet
    {
        type            inletOutlet;
        inletValue      uniform (0 0 0);
        value           uniform (0 0 0);
    }
Attached Images
File Type: png Screenshot from 2020-01-11 02-06-24.png (57.2 KB, 12 views)
File Type: jpg Screenshot from 2020-01-11 02-04-56.jpg (63.5 KB, 9 views)
Sedullo is offline   Reply With Quote

Old   January 11, 2020, 01:09
Default
  #2
Member
 
Geir Karlsen
Join Date: Nov 2013
Location: Norway
Posts: 59
Rep Power: 9
gkarlsen is on a distinguished road
Outlet BC for T should be inletOutlet if you want zeroGradient as flow goes out of the domain?
gkarlsen is offline   Reply With Quote

Old   January 11, 2020, 13:36
Default
  #3
Member
 
Alex
Join Date: May 2019
Posts: 35
Rep Power: 3
Sedullo is on a distinguished road
Hi gkarlsen, thanks for the reply.

I did as you said and actually that problem seems to be fixed, the temperature is high also at the outlet.
But now I have a new problem, I observe a strange phenomena, after 140 seconds I can see a sudden lowering of the temperature which lasts for about 10 seconds and afterwards it disappears.

I attach a picture of the steady situation (everything red at the outlet) and three pictures of the sudden lowering of temperature phenomena happening at the outlet.

What do you think could be the reason?
Sedullo is offline   Reply With Quote

Old   January 11, 2020, 14:21
Default
  #4
Member
 
Geir Karlsen
Join Date: Nov 2013
Location: Norway
Posts: 59
Rep Power: 9
gkarlsen is on a distinguished road
Looks like reverse flow, which you can confirm by looking at U in the direction of your outlet. If this is the problem it can be mitigated partly by using totalpressure BC instead of fixedvalue. Also you could take a look at:

https://www.cfd-online.com/Forums/op...ow-outlet.html
gkarlsen is offline   Reply With Quote

Old   January 13, 2020, 19:03
Default
  #5
Senior Member
 
Peter Hess
Join Date: Apr 2011
Location: Austria
Posts: 220
Rep Power: 12
peterhess is on a distinguished road
Hello!

Why the temperatures value in both inlet and outlet is 0?

That do not make much sense.

Increase (replace) those with 300...

---------------------------

At inlet use outletInlet

and

at outlet use inletOutlet

You have those reversed!

Regards

Peter
peterhess is offline   Reply With Quote

Old   January 13, 2020, 20:21
Default
  #6
Member
 
Alex
Join Date: May 2019
Posts: 35
Rep Power: 3
Sedullo is on a distinguished road
Hi Peter,

thanks for the suggestion, but actually nothing is changed, it is like that variable did not affect the final result.
Still have this backflow phenomena.

I attach also the bc for p and p_rgh to see if you can see here some problems

Code:
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    wall
    {
        type            calculated;
        value           $internalField;
    }

    #includeEtc "caseDicts/setConstraintTypes"
}
Code:
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    sideWallheated
    {
        type            fixedFluxPressure;
        rho             rhok;
        value           $internalField;
    }

    sideWallsNotheated
    {
        type            fixedFluxPressure;
        rho             rhok;
        value           $internalField;
    }


    inlet
    {
        type            totalPressure;
        p0              uniform 0;        
    }

    outlet
    {
        type            totalPressure;
        p0              uniform 0;        
    }

    #includeEtc "caseDicts/setConstraintTypes"
}
Sedullo is offline   Reply With Quote

Old   January 13, 2020, 21:00
Default
  #7
Senior Member
 
Peter Hess
Join Date: Apr 2011
Location: Austria
Posts: 220
Rep Power: 12
peterhess is on a distinguished road
Upload the case please!

Last edited by peterhess; January 13, 2020 at 22:03.
peterhess is offline   Reply With Quote

Old   January 13, 2020, 21:44
Default
  #8
Member
 
Alex
Join Date: May 2019
Posts: 35
Rep Power: 3
Sedullo is on a distinguished road
I uploaded the case, thanks for the help!
Attached Files
File Type: zip Project_wavy.zip (11.2 KB, 4 views)
Sedullo is offline   Reply With Quote

Reply

Tags
boundaries condition, temperature bc, velocity bc

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Impeller: temperature decreasing, should be increasing artymk4 OpenFOAM Running, Solving & CFD 20 June 5, 2020 16:13
Outlet temperature to temperature boundary condition of velocity inlet. (UDF) dillon Fluent UDF and Scheme Programming 3 March 25, 2018 11:06
outlet pressure Boundary settings -velocity streamline under ambient temp.conditions Vishnu_bharathi CFX 12 November 21, 2017 06:56
outlet temperature jigneshrohit99 FLUENT 1 March 25, 2016 13:26
Ansys CFX problem: unexpected very high temperatures in premix laminar combustion faizan_habib7 CFX 4 February 1, 2016 17:00


All times are GMT -4. The time now is 05:38.