[kcc49]

Hello, I am a new OpenFOAM user and currently working on how the effect of surface roughness affecting the impact introduced by dam break.

As a result, I am building a model through using the damBreak in OpenFoam Tutorial. Is there any way to introduce surface roughness into damBreak?

sincerely,
Jesse

[Phicau]

Hi Jesse,

you need to run the case with a turbulence model and specify nutkRoughWallFunction for nut.

Ks is the equivalent grain roughness (Nikuradse) and Cs is a roughness constant, check the details here: https://cpp.openfoam.org/v3/a01666.html#details

All this is put into play in the damBreakWithObstacle tutorial.

Best,

Pablo

[kcc49]

Originally Posted by Phicau

Hi Jesse,

you need to run the case with a turbulence model and specify nutkRoughWallFunction for nut.

Ks is the equivalent grain roughness (Nikuradse) and Cs is a roughness constant, check the details here: https://cpp.openfoam.org/v3/a01666.html#details

All this is put into play in the damBreakWithObstacle tutorial.

Best,

Pablo

thanks Pablo for your response!
However, I still not quite sure how to run the case with a turbulence model and specify nutkRoughWallFunction for nut.
Do you mind elaborate more?

Many thanks!
Jesse

[kcc49]

Originally Posted by Phicau

Hi Jesse,

you need to run the case with a turbulence model and specify nutkRoughWallFunction for nut.

Ks is the equivalent grain roughness (Nikuradse) and Cs is a roughness constant, check the details here: https://cpp.openfoam.org/v3/a01666.html#details

All this is put into play in the damBreakWithObstacle tutorial.

Best,

Pablo

Hello Pablo,

Does it mean all I need to do is to change the value of Ks and Cs (in bold text) nut file in file 0 in order to control the surface roughness?

boundaryField
{
atmosphere
{
type zeroGradient;
}

walls
{
type nutkRoughWallFunction;
Ks uniform 100e-6;
Cs uniform 0.5;
value $internalField;
}
}

[Phicau]

Exactly, select the appropriate values for your case and check damBreakWithObstacle tutorial if you can't make it work at first.

Pablo

[kcc49]

Many thanks for your help!

[kcc49]

Originally Posted by Phicau

Exactly, select the appropriate values for your case and check damBreakWithObstacle tutorial if you can't make it work at first.

Pablo

I have another question for building up the case

int the nut file, do i need to include those 'faces' as zeroGradient? see the following quote

atmosphere
{
type zeroGradient;
}

wall
{
type zeroGradient;
}

structure
{
type zeroGradient;
}

slope
{
type nutkRoughWallFunction;
Ks uniform 0.05;
Cs uniform 1;
value $internalField;
}
side
{
type empty;
}

[ing.nicola.dettole]

For velocity , pressure, k, epslion i have to use rough functions ?

[Nic86]

Hello. The nutkRoughWallFunction requires 3 entries:

Ks
Cs
value
What does it mean "value"?

For example In the dam break with obstacle tutorial the entries are:
Ks uniform 0.0001;
Cs uniform 0.5;
value uniform 5e-07;
What does it mean value uniform 5e-07?

Also what does
value $internalField
means?

Sorry for the stupid question but I cannot find valid documentation.
Thank you.

[mAlletto]

I'm not sure if the value is really required. It is written to the file since the nutwallfunctions are derived from the fidedValue boundary condition.

[Nic86]

Originally Posted by mAlletto

I'm not sure if the value is really required. It is written to the file since the nutwallfunctions are derived from the fidedValue boundary condition.

Hi,
I am quite sure that a value is needed because if i delete that line the code does not run and gives me error. It could be that the value is uninfluential when using the nutkwallfunctions but how can i be sure about it? Where can i find official reference about this function??
Thank you

[mAlletto]

You find some reference here:



https://www.openfoam.com/documentati...8H_source.html


https://www.openfoam.com/documentati...8C_source.html


some good explanation about wall functions in general (read the chapter standard wall function):



http://www.tfd.chalmers.se/~lada/pos..._report_WF.pdf


wall functions in openfaom


http://www.tfd.chalmers.se/~hani/kur...nfoamFinal.pdf


Unfortunately the nutkroughwallfunction is not described. But the only difference to the nutkwallfunction is the assumed velocity profile in the first cell adjacent to the wall.



Hope this helps


Best


Michael

[Nic86]

Excellent! Thank you!

[wind_]

Originally Posted by Phicau

Hi Jesse,

you need to run the case with a turbulence model and specify nutkRoughWallFunction for nut.

Ks is the equivalent grain roughness (Nikuradse) and Cs is a roughness constant, check the details here: https://cpp.openfoam.org/v3/a01666.html#details

All this is put into play in the damBreakWithObstacle tutorial.

Best,

Pablo

Do it need other Rough wall functions? such as nutURoughWallFunction