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

High negative pressure with interPhaseChangeFoam

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 22, 2013, 15:17
Default High negative pressure with interPhaseChangeFoam
  #1
New Member
 
Elio Bufi
Join Date: Jan 2013
Posts: 5
Rep Power: 4
legione is on a distinguished road
Hi Foamers,

I'm new in the OpenFoam world and I'm trying to study the cavitation phenomenon in a 3D simple, and very small, cylindrical duct (diameter 0.24 mm) that links two cubic capacities (one cube edge is long 6-7 mm more or less) .
The fluid is the same of Throttle Tutorial in CavitatingFoam Solver and the geometry system is similar (the substantial difference is that my case is 3D).
I'm running with interPhaseChangeFoam, laminar, because this is more accurate that CavitatingFoam, thanks to the implementation of VOF method . I've set pressure inlet (160 bar) and pressure outlet (1.5 bar) BC and wall on the other surfaces. The simulation seems to work fine, however when I try to visualize pressure p_rgh in paraFoam I find very high negative pressure (-60 bar more or less) in the initial circular section of the duct (where begin cavitation) , in the other regions the pressure values are positive. Are these negative values correct? When I achieve these negative pressure values the simulation goes ahead without problem, so I could think that this behavior is normal in a incompressible calculation....hope someone could help me in understand this. Thanks.
legione is offline   Reply With Quote

Old   January 24, 2013, 10:43
Default High negative pressure with interPhaseChangeFoam
  #2
New Member
 
Join Date: Aug 2012
Posts: 1
Rep Power: 0
alterfritz is on a distinguished road
I'm new in the OpenFoam world, too.

But raise up the nOuterCorrectors in fvSolution for more implicit calculations.
alterfritz is offline   Reply With Quote

Old   January 25, 2013, 07:46
Default
  #3
New Member
 
Elio Bufi
Join Date: Jan 2013
Posts: 5
Rep Power: 4
legione is on a distinguished road
Thank you so much alterfritz for your reply. Can you explain me how an increase of outer loop iterations can decrease the negative pressures? I have another theory. In my results I have noticed that the flow separates with a vortex in the negative pressure location. For this reason I could think that what I'm visualizing is not absolute pressure but a pressure gradient deltaP that becames negative because of the flow separation. But, in this case, my question is: what is the reference pressure for the pressure calculations? in the bottom I insert an image that explain better the situation of pressure (I have cut off the positive pressures so you can see only the negative pressures regions.). The flow goes from left to right.


Also I attach the p_rgh boundary condition in the 0 folder:

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.0.1 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [1 -1 -2 0 0];

internalField uniform 160e5;

boundaryField
{
inlet
{
type fixedValue;
value uniform 160e5;
U U;
rho rho;
psi none;
gamma 1;


}

outlet
{
type fixedValue;
value uniform 1.5e5;
}

wall
{
type zeroGradient;
}

cyl
{
type zeroGradient;
}

frontBack
{
type empty;
}
}

// ************************************************** *********************** //
legione is offline   Reply With Quote

Old   January 25, 2013, 07:48
Default
  #4
New Member
 
Elio Bufi
Join Date: Jan 2013
Posts: 5
Rep Power: 4
legione is on a distinguished road
sorry but the image seems don't work...try this link http://www.mediafire.com/view/?6ima64q5597ezcj
legione is offline   Reply With Quote

Old   April 8, 2013, 07:24
Default
  #5
abe
Member
 
ABE
Join Date: Jul 2012
Posts: 37
Rep Power: 5
abe is on a distinguished road
Hi,

I am using InterPhaseChange solver to simulate cavitation in OF2.1x
Although by old versions (i.e. OF1.5) I can get good results, with this new version results are not good at all. Dose anybody else get similar conflicts?

ABE
abe is offline   Reply With Quote

Old   April 11, 2013, 02:51
Default
  #6
Senior Member
 
Sandy Lee
Join Date: Mar 2009
Posts: 207
Rep Power: 9
sandy is on a distinguished road
Hi legione, I think, it is wrong if the pressure is negative in the internal field, because staturation pressure is higher so that it and water evaporate early.
sandy is offline   Reply With Quote

Old   July 4, 2013, 02:35
Default
  #7
Senior Member
 
sfigato's Avatar
 
Marco Longhitano
Join Date: Jan 2013
Location: Aachen
Posts: 103
Rep Power: 4
sfigato is on a distinguished road
Send a message via Skype™ to sfigato
Hi Foamers,

I am dealing with the same problem! I have a strong negative pressure where cavitation occurs! Legione have you found a solution?
Anyone can help me?

Thanks in advance
Regards
Marco
sfigato is offline   Reply With Quote

Old   July 5, 2015, 10:28
Default
  #8
Member
 
alvaro
Join Date: Apr 2015
Posts: 33
Rep Power: 2
alvariten is on a distinguished road
Hi all,

I know this thread is long time ago.. but, I have the same question and I've not found an explanation to negative pressure in the vortex zone (referred to interPhaseChangeFoam).
Somebody finally got a reasonable explanation?

Moreover, in my case I found that the velocity in the nozzle walls where cavitation occurs is not completely zero (It is of the order of 5-10 m/s). I have taken into consideration the mesh refinement in the wall region, but still not zero velocity. Anyone else has obtained these results?

Thanks.
Regards.
alvariten 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
high pressure boundary condition fragzilla CFX 5 September 14, 2012 02:40
Positive Pressure ang negative Pressure moca CFX 3 September 18, 2010 06:00
BlockMesh FOAM warning gaottino OpenFOAM Native Meshers: blockMesh 7 July 19, 2010 14:11
high pressure simulation mahi FLUENT 0 November 7, 2008 02:30
Axisymmetrical mesh Rasmus Gjesing (Gjesing) OpenFOAM Native Meshers: blockMesh 10 April 2, 2007 14:00


All times are GMT -4. The time now is 03:26.