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Old   October 19, 2010, 03:35
Lightbulb pressureInletOutletVelocity
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Hello Foamers,

I want to simulate a problem which i should set pressure at outlet. as it is not zeroGradient because it is not fully developed flow i should use another outlet type. i read user guide and i think this is a good choice:
HTML Code:
pressureInletOutletVelocity     Combination of pressureInletVelocity and inletOutlet
the question is what should i set for U outlet type?

Best regards,
Maysam
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Old   October 19, 2010, 04:34
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Depends on your boundary condition.

I pressume, this is just ordinary atmosphere kind outlet, right? In this case probably this will be the best choice

{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}
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Old   March 7, 2012, 07:46
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Quote:
Originally Posted by paka View Post
Depends on your boundary condition.

I pressume, this is just ordinary atmosphere kind outlet, right? In this case probably this will be the best choice

{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}

Hi...does it means we know the inlet pressure and we want to know outlet velocity by this by using this function?
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Old   March 7, 2012, 12:26
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Quote:
Originally Posted by maysmech View Post
Hello Foamers,

I want to simulate a problem which i should set pressure at outlet. as it is not zeroGradient because it is not fully developed flow i should use another outlet type. i read user guide and i think this is a good choice:
HTML Code:
pressureInletOutletVelocity     Combination of pressureInletVelocity and inletOutlet
the question is what should i set for U outlet type?

Best regards,
Maysam
when you use pressureInletOutletVelocity for U
you should use totalPressure for p

they are self-stabilizing bcs
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Old   March 15, 2012, 07:33
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Quote:
Originally Posted by calim_cfd View Post
when you use pressureInletOutletVelocity for U
you should use totalPressure for p

they are self-stabilizing bcs
Hi Mauricio,
but is seems in most case total pressure use in inlet and static pressure in outlet?
Also pressureInletOutletVelocity for U can be set in outlet? I was thiking it can only be set in inlet. I am confuse
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Old   March 15, 2012, 10:36
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the bcs i mentioned they kinda form a consistent pair and regarding the usage,, i guess you can use it for outlets, but then you have to handle the signs..

here's the description, guess you've seen it already.. i haven't tried it thou

pressureInletOutletVelocity
Code:
Description
    Velocity inlet/outlet boundary condition patches for where the pressure is
    specified.  zero-gradient is applied for outflow (as defined by the flux)
    and for inflow the velocity is obtained from the patch-face normal
    component of the internal-cell value.
pls give it a try if u have the time and keep us post!
ty
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Old   March 15, 2012, 10:45
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Quote:
Originally Posted by calim_cfd View Post
the bcs i mentioned they kinda form a consistent pair and regarding the usage,, i guess you can use it for outlets, but then you have to handle the signs..

here's the description, guess you've seen it already.. i haven't tried it thou

pressureInletOutletVelocity
Code:
Description
    Velocity inlet/outlet boundary condition patches for where the pressure is
    specified.  zero-gradient is applied for outflow (as defined by the flux)
    and for inflow the velocity is obtained from the patch-face normal
    component of the internal-cell value.
pls give it a try if u have the time and keep us post!
ty
Thanks Mauricio,

Where you found this description? Any other document besides the website?
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Old   March 15, 2012, 14:24
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the source code

go to your instalation directory (type "which icoFoam" in a terminal and u'll find the dir)

then open de *.H and *.C files. they have the descriptions. Search for the name you want, there will generally be a file with such name or very close one..

theres also a version @ http://www.openfoam.org/docs/cpp/ which has the same files in html
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Old   March 16, 2012, 09:03
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Yup! I found that but hv to go deep into scr!

http://www.openfoam.org/docs/cpp/
http://foam.sourceforge.net/docs/cpp/a04208_source.html

Quote:
Description
00027 Description
00028 Velocity inlet/outlet boundary condition for pressure boundary where the
00029 pressure is specified. zero-gradient is applied for outflow (as defined
00030 by the flux) and for inflow the velocity is obtained from the flux with
00031 the specified `inletDirection'.
00032
00033 Slip condition applied tangential to the patch.

Notice the last part ''.....for inflow the velocity is obtained from the flux with the specified `inletDirection'.'' Isnt it means if specified inlet direction it becomes pressureDirectedInletOutletVelocity


I have tried myself with specified outlet velocity with pressureDirectedInletOutletVelocity and inlet with zeroGradient. The simulation can run and vector velocity seems OK!

But I havent justified its correctness.

Now i try the reverse method inlet velocity pressureDirectedInletOutletVelocity and outlet zeroGradient then see both result.

Last edited by yipiyaya8; March 16, 2012 at 09:21.
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Old   November 16, 2012, 06:33
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Dear Friends,
I have a small problem, actually I got confused totally,
the think is i want to keep the total pressure as constant in my whole domain,
I have calculate that my Pd = 64.5Pa
now I want to implement this,
I want to give pressure inlet and pressure outlet

0/U
inlet
{
type pressureInletOutletVelocity;
value uniform (0 0 0) // what value i need to use here or is it ok?
}

0/p
inlet
{
type fixedValue;
}

outlet
{
type fixedValue;
value uniform 101325;
}

what is the condition I need to give for inlet?

thanks,
Aadhavan
Attached Files
File Type: txt p.txt (1.6 KB, 72 views)
File Type: txt U.txt (1.9 KB, 40 views)
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Old   November 16, 2012, 19:01
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hi, let me see if i got this right.. u want to keep the total pressure constant in the whole domain, yet you have a pressure difference (Pd??) of 65pa between inlet-outlet??? i'm sry but i think you need to re-think your problem a bit.. physically speaking... if the total pressure is even in the whole domain i guess there's no dynamics at all!? right? dude i say give your problem a thought and/or explain it better cuz they way u did it looks rly unreasonable..
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Old   November 17, 2012, 08:19
Default fan simulation
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Hi Fomers and Calim;

I am simulating a fan using MRFSimpleFoam,
I have given the boundary condition as follows,
0/U

inlet
{
type flowRateInletVelocity;
flowRate 2;
value uniform (0 0 0);
}
outlet
{
type zeroGradient;
}

0/P

inlet
{
type zeroGradient;
}

outlet
{
type fixedValue;
value uniform 101325;
}

the simulation ran upto 10000 Iteration,
I have attached the Residual plot as well, please have a look.
but the result is not matching with experimental result.

actually inlet pressure should be less than outlet pressure but I an getting other way around.

I am trying to fix this issue by giving different BC as follows,

0/U

outlet
{
type zeroGradient;
}
inlet
{
type pressureInletOutletVelocity;
value uniform (0 0 0)

0/p

inlet
{
type totalPressure;
gamma 0;
p0 uniform 101325; // total pressure
value uniform 101325;
}

outlet
{
type fixedValue;
value uniform 101260.5; // static pressure
}

while execute the solver, I am getting the following error,

Create mesh for time = 0

Reading field p

Reading field U



--> FOAM FATAL IO ERROR:
Cannot find patchField entry for cyclic ILR0
Is your field uptodate with split cyclics?
Run foamUpgradeCyclics to convert mesh and fields to split cyclics.

file: /home/cerecam/OpenFOAM/OpenFOAM-2.0.1/tutorials/incompressible/MRFSimpleFoam/exCompDomain/onlyPressure/0/U::boundaryField from line 25 to line 76.

From function GeometricField<Type, PatchField, GeoMesh>::
GeometricBoundaryField::GeometricBoundaryField
(
const BoundaryMesh&,
const DimensionedField<Type, GeoMesh>&,
const dictionary&
)
in file /home/cerecam/OpenFOAM/OpenFOAM-2.0.1/src/OpenFOAM/lnInclude/GeometricBoundaryField.C at line 271.

FOAM exiting


please guide me how to approach this problem,
I am really struggling to solve this problem.
please help me,

thanks,
Aadhavn
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Old   January 21, 2013, 08:34
Default what should be the value for pressureInletOutlet bc
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I want to use pressureinletoutletVelocity boundary condition for velocity at outlet as this is not fully developed (there is a chance to be backflow) flow. But my question is what the value I should set? Is it always (0 0 0)? What is the function of this fixed value of velocity?

type pressureInletOutletVelocity;
value uniform (0 0 0)
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Old   January 27, 2013, 02:51
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It seems the velocity you prescribe is only for the tangential component of the boundary....I do not think you specify the normal velocity to the boundary... I will look more into this.
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Old   April 11, 2013, 11:29
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Hi to all
Someone know how velocity is obtained from pressure in pressureInletOutletVelocity?

thank to all
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Old   July 28, 2013, 14:15
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hello
I want to use the pressureInletOutletVelocity for the outlet of the airfoil boundary condition.
But I donít the mean of tangent velocity?and What is the difference between value and tangential velocity?</SPAN>
Is this value scalar or vector?
thanks
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Old   July 28, 2013, 16:43
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Hi,
why you want use this boundary condition for airfoil? I think that this boundary condition have to be used with multiphase flow or when in the same boundary you have an inlet and outlet flux. This is your case?
Anyway a zeroGradient condition is applied for outflow; for inflow, the velocity is obtained from the patch-face normal component of the internal-cell value.
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Old   July 28, 2013, 16:49
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Quote:
hello
I want to use the pressureInletOutletVelocity for the outlet of the airfoil boundary condition.
But I donít the mean of tangent velocity?and What is the difference between value and tangential velocity?</SPAN>
Is this value scalar or vector?
thanks


hi
pressureinletoutletvelocity (in) bcs are to be used with inletoutlet (out) bcs for the u field

and you use totalpressure(in) and fixedvalue(out) for the p field

these bcs guarantee a well-posed problem in case the user has only pressure measures and backflow expected

try that
l8r and gl
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Old   July 28, 2013, 16:51
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just to add,

if these bcs are the best ones for your case that's a whole new ball game!
l8r
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Old   July 29, 2013, 04:48
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hi dear mauricio
thanks for your answer.
But I did not answer my question:
What is the difference between value and tangential velocity?Is this value scalar or vector?
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