[otaolafr]

Originally Posted by TanF

Hello everyone!
I am currently working with OpenFoam to create a cylinder. The cylinder I need should only be discretized in the h direction (Photo). Does anyone know how I can avoid the round basement being divided into so many small cells? (I have attached a photo).
I´m quite new to OpenFoam and would be very happy if someone could help me!
Regards!

hello,

mm from what i have read about the subject, in OpenFOAM the cylinder is created from adding an arc section to a square section. but from your post:
i do not get why you need this ? (are you trying to simulate a 2D simulation?)
at least from what i know in of doing a cylinder with only separation in the axis, would not be possible...but i insist that i can not imagine why you would like to do that (i am new to CFD so maybe i am not following you..) maybe if you explain me a little bit more i could help you more
best regards.

[TanF]

Hi Otaolafr,
Thank you for your answer!
I try to do this because I need a cylinder mesh for simulations with an other program. In this other program the simulation time is very long if I have so many cells - maybe there is a way to connect the cells on the round basement?
And beside of that I need to be able to fix the initial parameters of the cells on one side of the cylinder and I can't fix so many...
Also I have researched whether there is a possibility to connect all cells of the grid to one cell but so far I do not think that works ...Maybe you have an idea? I would be very grateful!

[otaolafr]

Originally Posted by TanF

Hi Otaolafr,
Thank you for your answer!
I try to do this because I need a cylinder mesh for simulations with an other program. In this other program the simulation time is very long if I have so many cells - maybe there is a way to connect the cells on the round basement?
And beside of that I need to be able to fix the initial parameters of the cells on one side of the cylinder and I can't fix so many...
Also I have researched whether there is a possibility to connect all cells of the grid to one cell but so far I do not think that works ...Maybe you have an idea? I would be very grateful!

mmmm... you need a surface mesh? an .stl? i dont know what program, i find it strage that you need a cylinder with a one only cell in the r direction. sadly no, i can not imagine how to do it, at least you are going to have five cells.have a look here (credits to wolfdynamics) page 59/60 http://www.wolfdynamics.com/images/O..._blockmesh.pdf

[TanF]

Oh I'm sorry, I don't need a cylinder with just one cell. I just thought that maybe there is a command that can unify all of them, that would solve the problem of having so many. Having a mesh with 5 cells would be alright... What I need is a cylinder that has just one cell in the round basement and not thousands like in the picture of the mesh I posted. And additionally it would be perfect if the mesh would only be discretized in one direction - that is all I want ☺️ but I think that is to much wanted! 😐

[guin]

Following alternative may be of interest for some visitors of this thread:

Simple cylindrical geometry: example using blockMesh

PS: IMHO the proposed whole-cylinder with inner wedged elements may lead to numerical troubles along the axis... Therefore I'd rather recommend to use hex-elements whenever possible. Most algorithms will behave more gracefully!

[HPE]

I once found the following relevant script from Ehsan Madadi, might be useful for some of you to generate cylinder meshes with OpenFOAM:

https://www.ehsanmadadi.com/cylinder-mesh/

[Bloerb]

A simple example

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 1;
pri   0.20; // positiv inner radius
pxm   0.12; // postiv x value for smooth transition on inner rectangle
pra   0.325; // positve outer radius
nxm   #neg $pxm; // #neg only works in foundation version
nri   #neg $pri; // #neg only works in foundation version
nra   #neg $pra; // #neg only works in foundation version

leA   0.785; // upper z value 
leB   0.0;   // lower z value 

pa 25; // number of cells in angle phi direction(per block) or 4*pa around circumference. inner rectangle pa*pa 
ra 10; // number of cells in radial direction
za 50; // number of cells along the height


vertices
(   
  name i0 (0    $nri $leA)
  name i1 ($pri 0    $leA)
  name i2 (0    $pri $leA)
  name i3 ($nri 0    $leA)
  
  name a0 (0    $nra $leA)
  name a1 ($pra 0    $leA)
  name a2 (0    $pra $leA)
  name a3 ($nra 0    $leA)  
  
  name I0 (0    $nri $leB)
  name I1 ($pri 0    $leB)
  name I2 (0    $pri $leB)
  name I3 ($nri 0    $leB)
  
  name A0 (0    $nra $leB)
  name A1 ($pra 0    $leB)
  name A2 (0    $pra $leB)
  name A3 ($nra 0    $leB)   
);

blocks
(
  hex (i3 i2 i1 i0 I3 I2 I1 I0) myCellZone ($pa $pa $za) simpleGrading (1 1 1)     
  hex (i0 i1 a1 a0 I0 I1 A1 A0) myCellZone ($pa $ra $za) simpleGrading (1 1 1)    
  hex (i1 i2 a2 a1 I1 I2 A2 A1) myCellZone ($pa $ra $za) simpleGrading (1 1 1)    
  hex (i2 i3 a3 a2 I2 I3 A3 A2) myCellZone ($pa $ra $za) simpleGrading (1 1 1) 
  hex (i3 i0 a0 a3 I3 I0 A0 A3) myCellZone ($pa $ra $za) simpleGrading (1 1 1)  
);

edges
(

 spline i0 i1  (($pxm $nxm $leA))  # spline on inner square to round it for improved mesh quality  
 spline i1 i2  (($pxm $pxm $leA))
 spline i2 i3  (($nxm $pxm $leA))
 spline i3 i0  (($nxm $nxm $leA))

 spline I0 I1  (($pxm $nxm $leB)) 
 spline I1 I2  (($pxm $pxm $leB))
 spline I2 I3  (($nxm $pxm $leB))
 spline I3 I0  (($nxm $nxm $leB))

 arc a0 a1  90 (0 0 1)   # works in the foundation version  
 arc a1 a2  90 (0 0 1)
 arc a2 a3  90 (0 0 1)
 arc a3 a0  90 (0 0 1)   

 arc A0 A1  90 (0 0 1)    
 arc A1 A2  90 (0 0 1)
 arc A2 A3  90 (0 0 1)
 arc A3 A0  90 (0 0 1)  
);
   
defaultPatch
{
    name allBoundary;
    type wall;
}   

boundary
(  
);