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Old   December 15, 2009, 12:10
Default
  #41
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Hi Matteo,

You mean nut, right? I have the following:

HULL
{
type nutWallFunction;
value uniform 0;
}

Gonzalo
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Old   December 16, 2009, 01:29
Default simulation in local heat transfer downstream of an abrupt expansion
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hassan
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Good Day

Please I need your help

I want simulation in local heat transfer downstream of an abrupt expansion in a circular channel with a constant wall heat flux


Fluid air and turbulent flow and fully developed
Reynolds no =5300 to 87000

I will change diameter ratio\


I want simulate by used CFD fluent

Objective of the study

Present research purpose is to obtain detail heat transfer coefficient and surface temperature downstream of an abrupt expansion pipes, and to investigate the flow of an abrupt expansion pipe for the different pipe to test section ratio (D/d) and different range of Reynolds number.
The research will concentrate of the phenomena effecting parameter such as wall heat flux, air flow velocity and the separation step height.
wich best in this case K-epsilon Or K- omega and which model


Scope of the study

The aim present work is to simulate by using CFD Fluent 6.3 the effect of flow separation on heat transfer process for the axisymmetric, turbulent separated flow in an annular passage. The air flow separation in induced by different height of a circular steps by reduction the outer annular tube diameter upstream of the heated test section. Reattachment and redevelopment of the flow occurred behind the point of separation. The test heated pipe is electrically, where, the experiments provide a constant heat Flux ranged from about 80 W/m2 to 720 W/m2 for each step. The degree of the separation is varied by using different tubes diameter of heating section which provided height steps ratio range varied from (0.2671).The Reynolds number Red encompassed a range from about 5300 to 87000 it was varied by change air velocity by changing gate position for blower


Thank you so much

hassan

Master student

UPM University

Malaysia


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Old   December 16, 2009, 09:56
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  #43
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Hi hassan,

I see that you're using Fluent. In order to keep things focused, it would be great if you can copy your post and make a new thread about it in the Fluent forum. There's lot of people there with more experience in that package willing to help you. Don't forget to remove it from here.

Regards,

Gonzalo
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Old   December 16, 2009, 10:08
Default Forces
  #44
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Well, this is how thing are going today...

First of all, many thanks to Matteo who came up yesterday with a modification in the interFoam solver to make it work with the new force function. Now I think the forces are correctly calculated, which doesn't mean they're correct though.

Now there's a rho file in the \0 folder. I found it was necessary to initialized it the same way we do for alpha, otherwise it diverges. The viscous forces have improved significantly, but we are still way off. I attach the force convergence plots until 5s.

wigley_286_force_plots-0.png

wigley_286_force_plots-1.png

wigley_286_force_plots-2.png

wigley_286_force_plots-3.png

As I already investigated lots of variables, now I wonder if the wall function is defined properly. This is my nut and nuTilda, any idea?

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.6 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -1 0 0 0 0];

internalField uniform 0;

boundaryField
{
OUTLET
{
type calculated;
value uniform 0;
}
SYMMETRY
{
type symmetryPlane;
}
ATMOSPHERE
{
type calculated;
value uniform 0;
}
EXTRAHULL
{
type nutWallFunction;
value uniform 0;
}
INLET
{
type calculated;
value uniform 0;
}
HULL
{
type nutWallFunction;
value uniform 0;
}
}


// ************************************************** *********************** //

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.5 |
| \\ / A nd | Web: http://www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object nuTilda;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -1 0 0 0 0];

internalField uniform 0.0009;

boundaryField
{
OUTLET
{
type zeroGradient;
}
SYMMETRY
{
type symmetryPlane;
}
ATMOSPHERE
{
type fixedValue;
value uniform 0.0009;
}
EXTRAHULL
{
type zeroGradient;
}
INLET
{
type fixedValue;
value uniform 0.0009;
}
HULL
{
type zeroGradient;
}
}


// ************************************************** *********************** //
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Old   December 16, 2009, 10:51
Default
  #45
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olivier braun
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As there is this thread open about problems with inter...Foam, I try it here before opening a new one.
First I have to admit we are mot very experiences with the VOF implementation in OpenFOAM and i do not have the time to go through all sources to understand how volume fraction conservation is treated with dynamic meshes.
Did anyone encounter a similar problem to what we found in interDyMFoam for simulating a falling wedge, using a procedure similar to the dynamicInkJetMesh, compressing the mesh under the wedge while the wedge region does a translation, air is blown out through an outlet at the top.
As the mesh cells in the pure water region are compressed, the alpha goes well beyond one. Its value does not correspond to the inverse compression ratio precisely, but same order of magnitude... for the mesh volumes compressed to 75% of their initial volume the alpha1 value reaches 1.6. Any explanation for this ? Though the simulation does not blow up, it maintains this pretty unphysical level of alpha over hundreds of timesteps.
Is there something to add to our custom mesh motion routine to correct alpha1? In the style of the CorrectBoundary for the boundary motion ?
Questions over questions. Think we will not resolve them before the deadline of the students project which is tomorrow, but I am anyway interested in any input about the subject.

Cheers

Olivier
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Old   December 16, 2009, 12:06
Default k and omega too
  #46
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As I was pasting nut and nutilda I will do the same with omega and k just in case someone finds the problem.

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.6 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object k;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0.0038;

boundaryField
{
OUTLET
{
type zeroGradient;
}
SYMMETRY
{
type symmetryPlane;
}
ATMOSPHERE
{
type inletOutlet;
inletValue uniform 0.0038;
value uniform 0.0038;
}
EXTRAHULL
{
type kqRWallFunction;
value uniform 0.0038;
}
INLET
{
type fixedValue;
value uniform 0.0038;
}
HULL
{
type kqRWallFunction;
value uniform 0.0038;
}
}


// ************************************************** *********************** //

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.6 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object omega;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 0 -1 0 0 0 0];

internalField uniform 4.38;

boundaryField
{
OUTLET
{
type zeroGradient;
}
SYMMETRY
{
type symmetryPlane;
}
ATMOSPHERE
{
type inletOutlet;
inletValue uniform 4.38;
value uniform 4.38;
}
EXTRAHULL
{
type omegaWallFunction;
value uniform 4.38;
}
INLET
{
type fixedValue;
value uniform 4.38;
}
HULL
{
type omegaWallFunction;
value uniform 4.38;
}
}


// ************************************************** *********************** //
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Old   February 23, 2010, 04:17
Default how can i deleted
  #47
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hi how can i deleted
Quote:
Originally Posted by g.redondo View Post
Hi hassan,

I see that you're using Fluent. In order to keep things focused, it would be great if you can copy your post and make a new thread about it in the Fluent forum. There's lot of people there with more experience in that package willing to help you. Don't forget to remove it from here.

Regards,

Gonzalo
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Old   April 7, 2010, 13:03
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  #48
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Francisco Miguel
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Hello,

May I ask how did you finally solve the problem for the forces?

If the forces library is easy to modify, I think a simple approach will be to neglect the aerodynamic drag by multiplying the forces on each cell by gamma before integration, but I have no idea of how to compile solvers.

Right now I am using the 1.5 distribution included in caelinux, I don't know if it is worth the effort to update to version 1.6.

Thanks in advance,

Francisco
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Old   April 7, 2010, 15:09
Default how can i remove plz
  #49
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how can i remove plz
Quote:
Originally Posted by g.redondo View Post
Hi hassan,

I see that you're using Fluent. In order to keep things focused, it would be great if you can copy your post and make a new thread about it in the Fluent forum. There's lot of people there with more experience in that package willing to help you. Don't forget to remove it from here.

Regards,

Gonzalo
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Old   April 17, 2010, 01:38
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Dan, Mai-Chi and Marion
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Hello all,

I'm attempting to model a planing hull at the free surface of water.

I'm using rasInterFoam in v1.4.1 with k-omega SST turbulence modelling.

To get the boundary conditions right I'm trying to get a very simple case working (two-phase flow around a block at the air-water interface) with a constant velocity inlet (one inlet patch for air, one for water), a no-slip body and zeroGradient pd at the outlet and domain walls.

Unfortunately, after a few time steps the Courant number just increases and keeps increasing. It appears the problem starts around the interface.

I assume there's something wrong with my boundary conditions - what would be the recommended BCs? Has anyone else had this problem?

Any help would be gratefully received.

Regards,
Marion
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Old   April 17, 2010, 03:34
Default how can i remove plz
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how can i remove plz
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Old   April 22, 2010, 00:56
Default help
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hi everyone
I have a new solver for two-phase modeling. but there is a problem while running any case (dam break for instance). when in ControlDict I put the write interval one second the solution diverge quickly but if I put it .05 second the solution converges. I could not understand how the write interval affects the convergence of the system.
please help as soon as possible
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Old   April 23, 2010, 13:11
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What's the status of 1.6 validation? Has anyone managed to get a good agreement between 1.5 and 1.6 results with the new p formulation?

Eric, are you still running in 1.5? If the trend is to keep p instead of pd what's the plan?

Regards,

Gonzalo
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Old   April 23, 2010, 13:40
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Hi,

I am going to try to get something running within the next few days with 1.6, in order to see what happens... Not very optimistic about it though.
I finally did not manage to get the forces function working with 1.5, my version crashed... as did the original forces function, for some reason I got an error of "trying to read boynd EOF"... So I can not compare with 1.5 results unless I find a way of fixing this... any clues?

Regards,

Francisco
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Old   April 23, 2010, 14:23
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  #55
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Hi Gonzalo,

I primarily use 1.5-dev, because of the fact that there is quite a bit of technology in the OpenFOAM-extend project that I find useful. However, I also have 1.6.x installed on my various machines.

With that said, I don't like working with total pressure because it mucks up the boundary conditions. As such, in 1.6, I've converted interFoam back to dynamic (or piezometric) pressure, which then permits use of zero-gradient conditions on pd.

Eric
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Old   April 24, 2010, 09:18
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Thank you Eric,

It would be nice to know what the developers think about our problems with total pressure. I will give up with p and go back to 1.5, but I don't like to be working with something that might not be the trend in future versions. Anyway, the way it is right now is not an option.

Regards,

Gonzalo
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Old   April 24, 2010, 19:47
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Hi Eric,

One more thing. Hope I'm not asking too much. Could you explain me how to convert in 1.6 back to dynamic pressure?

Best regards,

Gonzalo
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Old   May 18, 2010, 05:27
Default Face flux field
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Dear all,


I tried the tutorial "wigley" by Prof. Paterson. If I am right, this one uses the non-turbulent interFoam solver from version 1.5.

In the the 0/ folder, the face flux field is already defined with nonuniform values in the internalField and on the boundaries XMIN and XMAX. Where do these values come from? And how can I define them myself for another simulation?
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Old   June 4, 2010, 05:20
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Hi everyone,

I'm trying to get a simulation of wake from an stl file, and I have some troubles, my velocity becomes very high on the hull front very quickly, at 0.04s , may be someone could help me :

-- I have a 150 (-40 to 110 ) x 50 (w -25 to 25) x 30 (d -15 to 15) domain
-- My stl file is a little boat found on internet, ref BoatN100708
-- I use snappyHexMesh and my refinment level is quite good : level (5 6)
-- My boundary conditions for the boat are :
zerogradient for alpha1
fixedValue value uniform (0 0 0) for U
buoyantPressure for p
-- The water velocity is initialize to (-10 0 0) (so negative speed is normal)
-- I use interFoam

Here are the pictures, any ideas ?
Attached Images
File Type: jpg wireframe.jpg (96.5 KB, 186 views)
File Type: jpg velocity.jpg (59.8 KB, 173 views)
File Type: jpg alpha1.jpg (41.0 KB, 196 views)
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Old   June 4, 2010, 17:17
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Hi yannH,

I would refine the mesh much more. Try to use a volumetric control at the free surface so you have more cells in there.

Enjoy,

Gonzalo
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