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

definition of totalPressure

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 5, 2013, 11:18
Default definition of totalPressure
  #1
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,174
Rep Power: 16
immortality is on a distinguished road
in the totalPressure BC at this part:
Code:
if (psiName_ == "none" && rhoName_ == "none")
    {
        operator==(p0p - 0.5*(1.0 - pos(phip))*magSqr(Up));
    }
    else if (rhoName_ == "none")
    {
        const fvPatchField<scalar>& psip =
            patch().lookupPatchField<volScalarField, scalar>(psiName_);

        if (gamma_ > 1.0)
        {
            scalar gM1ByG = (gamma_ - 1.0)/gamma_;

            operator==
            (
                p0p
               /pow
                (
                    (1.0 + 0.5*psip*gM1ByG*(1.0 - pos(phip))*magSqr(Up)),
                    1.0/gM1ByG
                )
            );
        }
        else
        {
            operator==(p0p/(1.0 + 0.5*psip*(1.0 - pos(phip))*magSqr(Up)));
        }
there is this well-known formula.but there is some questions
1) why "(1.0 - pos(phip))" term is put in this formula?what it means?
2)does Up and psip stand for internalField(p) and 1/(R*internalField(T))?
Code:
p0p
               /pow
                (
                    (1.0 + 0.5*psip*gM1ByG*(1.0 - pos(phip))*magSqr(Up)),
                    1.0/gM1ByG
3)I have written this formula(isentropic relation) in groovyBC in this manner:
Code:
p0_2/pow(1+(gamma-1)/2*magSqr(internalField(U))/(gamma*R*internalField(T)),3.5)
is it equivalent correctly to what there is in OF totalPressure code?
immortality is offline   Reply With Quote

Old   March 5, 2013, 11:31
Default
  #2
Senior Member
 
Join Date: Nov 2009
Location: Michigan
Posts: 135
Rep Power: 7
doubtsincfd is on a distinguished road
We had some discussion on the total pressure bc sometime back.
See if it helps you:

Negative absolute pressure in rhoPorousMRFSimpleFoam
doubtsincfd is offline   Reply With Quote

Old   March 5, 2013, 13:04
Default
  #3
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,174
Rep Power: 16
immortality is on a distinguished road
thanks a lot.
then its incorrect to set totalPressure at outlet?
I have 2 totalPressure BC at inlet and outlet.at inlet it behaves somewhat good(except supersonic velocity at 3-4 begining time steps that should be subsonic in real but it modifies at later time steps and becomes subsonic) but when outlet opens pressure goes too little and velocity increases a lot and problem diverges.
could anyone argue about the formula I have written at above post?
thanks.
immortality is offline   Reply With Quote

Old   March 8, 2013, 04:58
Default
  #4
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,174
Rep Power: 16
immortality is on a distinguished road
any more remarks?
immortality is offline   Reply With Quote

Old   March 8, 2013, 09:59
Default
  #5
Senior Member
 
Join Date: Nov 2009
Location: Michigan
Posts: 135
Rep Power: 7
doubtsincfd is on a distinguished road
Hi Ehsan,

Regarding the bcs, I have replied on Negative absolute pressure in rhoPorousMRFSimpleFoam

I also faced the similar problem i.e velocity going supersonic and solution blowing up. I then changed the relaxation parameters suggested by niklas in the post mentioned above.

In my case, I monitored the absolute pressure at inlet and it went negative for first few iterations. Are you experiencing the same problem?
doubtsincfd is offline   Reply With Quote

Old   March 8, 2013, 19:45
Default
  #6
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,174
Rep Power: 16
immortality is on a distinguished road
i set fixedValue at outlet and it fixed the problem!
But in inlet the issue is remain and because my case is transient i think its important and i can't use relaxations.i tried to limit velocity by groovyBC but i didn't have any effect.
I'll be glad if you let me know your progress.
immortality is offline   Reply With Quote

Old   March 9, 2013, 22:13
Default
  #7
Senior Member
 
Join Date: Nov 2009
Location: Michigan
Posts: 135
Rep Power: 7
doubtsincfd is on a distinguished road
I was using simpleFOAM (steady state) and so was not concerned with the transient solution

the relaxation factors prevented solution from blowing up but the problem for first few iterations still persists
doubtsincfd is offline   Reply With Quote

Old   March 15, 2013, 05:38
Default
  #8
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,174
Rep Power: 16
immortality is on a distinguished road
did anyone find a way or have an idea to limiting velocity at initial iterations when using total pressure at inlet?
immortality is offline   Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Totalpressure Ansys Leuchte CFX 2 April 9, 2013 18:56
(AutoGRID 5) Problem in Geometry definition of propeller venkat_aero2007 NUMECA 14 July 31, 2012 14:05
BC settings to expand pressure on atmosphere - simpleFoam / totalPressure sErik OpenFOAM Running, Solving & CFD 1 June 15, 2011 02:49
OpenFOAM static build on Cray XT5 asaijo OpenFOAM Installation 9 April 6, 2011 12:21
OpenFOAM14 for Mac OSX Darwin 104 gschaider OpenFOAM Installation 118 July 20, 2008 05:19


All times are GMT -4. The time now is 16:30.