[hfs]

Hello!

I am using the turbineSiting tutorial to help me understand how to implement a rough wall boundary conditions

I tried to change the Ks value in the nut file in 0 folder from 0.2 to 200 ,,, but it is giving me the same velocity field every time ... is this nutkRoughWallFunction really working??

Please see the attached photos!

Thanks a lot for your explanation!

[zandi]

Originally Posted by hfs

Hello!

I am using the turbineSiting tutorial to help me understand how to implement a rough wall boundary conditions

I tried to change the Ks value in the nut file in 0 folder from 0.2 to 200 ,,, but it is giving me the same velocity field every time ... is this nutkRoughWallFunction really working??

Please see the attached photos!

Thanks a lot for your explanation!

I have the same question

[wyldckat]

Greetings to all!

Originally Posted by zandi

I have the same question

Which OpenFOAM version are you using? It's indeed possible that this is a bug and it also might have already been fixed in more recent versions.

Best regards,
Bruno

[zandi]

Originally Posted by wyldckat

Greetings to all!


Which OpenFOAM version are you using? It's indeed possible that this is a bug and it also might have already been fixed in more recent versions.

Best regards,
Bruno

Thank you very much it was my fault. but now I have another problem. due to maning formula the water level has been compared to simulated water level.
but there is a big difference.
Maning formula --> y0=0.0429
simulated ----> y0=0.058

OpenFOAM 2.3.0
solver=interFoam
n(maning)=0.011 ----> Ks=0.3 mm
Cs=0.5
s=tan 2.5
L=2mm
q=0.1 m^3/s/m

is there any reason?
Regards,
zandi

[wyldckat]

Hi zandi,

Sorry, I'm not familiar with this topic and therefore have no idea in what context those parameters are applied I don't know or at least don't remember reading about the "Maning formula".

I need more details on how those values are being used in your case in OpenFOAM, so that I can check if there is something wrong with the units used in "nutkRoughWallFunction".

In addition: please keep in mind that I can't see what you're seeing, unless you share it. See the following thread for checking what kind of information I'm looking for: http://www.cfd-online.com/Forums/ope...-get-help.html

It's also possible that you're using incorrect boundary conditions.

Best regards,
Bruno

[zandi]

Thank you Bruno.

Maning formula give us the water level according to roughness and I want to compare my simulation result with that.

The domain is 2D and 1 or 2 mm cell size. Slope is 0.04366.
I give Ks=0.0003 m and Cs=0.5 to OF.
I set water fields and give volume inflow rate (Q/b=0.1m^3/s/m) in include folder (initial condition). K-Epsilon is used.
in case with no roughness water level has been obtained 56 mm and with roughness 58 mm
But it has to bee about 43 mm

BCs are:

 /*--------------------------------*- C++ -*----------------------------------*\
 
FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
#include "include/initialConditions"
dimensions [0 1 -1 0 0 0 0];
internalField uniform (0 0 0);
boundaryField
{
w-inlet
{
type variableHeightFlowRateInletVelocity; 
flowRate $inletFlowRate;
alpha alpha.water;
value uniform (0 0 0);
 
 
}
outlet
{
type zeroGradient; 
}
walls
{
type fixedValue;
value uniform (0 0 0);
}
 
atmosphere
{
type pressureInletOutletVelocity;
phi phi;
value uniform (0 0 0);
}
"(defaultFaces|Front|Back)"
{
type empty;
}
}
// ************************************************************************* //

 /*--------------------------------*- C++ -*----------------------------------*\
 
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
#include "include/initialConditions"
dimensions [1 -1 -2 0 0 0 0];
internalField uniform $pressure;
boundaryField
{
w-inlet
{
type zeroGradient;
}
outlet
{
type zeroGradient; }
walls
{
type zeroGradient;
}
 
atmosphere
{
type totalPressure;
p0 uniform 0;
U U;
phi phi;
rho none;
psi none;
gamma 1;
value uniform $pressure;
}
"(defaultFaces|Front|Back)"
{
type empty;
}
}
// ************************************************************************* //

 /*--------------------------------*- C++ -*----------------------------------*\
 
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions [0 2 -1 0 0 0 0];
internalField uniform 0;
boundaryField
{
w-inlet
{
type calculated;
value uniform 0;
}
outlet
{
type calculated;
value uniform 0;
}
walls
{
type nutkRoughWallFunction;
value uniform 0;
Ks uniform 0.0003;
Cs uniform 0.5;
}
 
atmosphere
{
type calculated;
value uniform 0;
}
"(defaultFaces|Front|Back)"
{
type empty;
}
}
 
// ************************************************************************* //

/*--------------------------------*- C++ -*----------------------------------*\
 
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object alpha.water;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
#include "include/initialConditions"
dimensions [0 0 0 0 0 0 0];
internalField uniform 0;
boundaryField
{
w-inlet
{
type variableHeightFlowRate; 
lowerBound 0.0;
upperBound 0.9;
value uniform 0;
 
}
outlet
{
type zeroGradient;
}
walls
{
type zeroGradient;
}
atmosphere
{
type inletOutlet;
inletValue uniform 0;
value uniform 0;
}
"(defaultFaces|Front|Back)"
{
type empty;
}
}
// ************************************************************************* //

[vatavuk]

Hi Zandi,
Manning's equation is valid for uniform steady flow. Are you sure that the length of the channel is adequate for the flow to become uniform?
And about the simulation time, is it enough for the flow to become steady?
You are doing an interesting simulation. If you could send the complete setup of the case, I would be interested.
Best Regards,
Paulo

[zandi]

Originally Posted by vatavuk

Hi Zandi,
Manning's equation is valid for uniform steady flow. Are you sure that the length of the channel is adequate for the flow to become uniform?
And about the simulation time, is it enough for the flow to become steady?
You are doing an interesting simulation. If you could send the complete setup of the case, I would be interested.
Best Regards,
Paulo

Hi friend thank you
you are right.
But the simulation had got steady before I took the result data. and almost uniform!!
even though
I have done the calculation with simple step by step method too and in that length with start water level as the simulation 0.055 m, water level has been obtained 0.0446! and when it reached to almost uniform level is 0.0477 (with difference less than 0.001 in 0.2 meter distance of channel) and 0.304 (with difference less than 0.0001 in 0.2 meter distance of channel) and as you can see it is different with simulation too.
There is no more especial specification about simulation.
sorry for not sending complete case, it is my little project. but you can do it with what I explained in the post

[wyldckat]

Greetings to all!

@zandi: I've finally managed to come back to your question... but unfortunately I do not have enough time to set-up a case similar to yours.
If you're still interested to find the solution for this issue, then please provide a simple test case, because I don't have enough free time to prepare one myself; nor was I able to figure out what might be wrong, only by looking at the files you've provided.

Best regards,
Bruno

[zandi]

Dear friends specially Bruno,

thanks for help,

I think I found the answer but forget to post here. It is because of not getting uniform as our fiend said.
however actually I expect when I give the uniform depth at inlet, it has to be uniform. but it seems it can't be so and need to get uniform at a length more than previous length I had given. why it is like that ?

I will send the simple case next time I'd log on.

Regards,
zandi