[ShanuNith]

Hi everyone,
I have a doubt in my mind, how do i know the axis direction of my rotating cylinder.

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 7
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volVectorField;
location "0";
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform (0 0 0);

boundaryField
{
leftWall
{
type noSlip;
}
rightWall
{
type noSlip;
}
lowerWall
{
type noSlip;
}
atmosphere
{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}
cylinder1Wall
{
type rotatingWallVelocity;
origin (-0.035 0 -1);
axis (0 0 1);
omega constant -2; //rad per sec
}
cylinder2Wall
{
type rotatingWallVelocity;
origin (0.035 0 1);
axis (0 0 1);
omega constant 2; //rad per sec
}
defaultFaces
{
type empty;
}
}


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

i have two cylinders of which the first cylinder is at left and second is at right. Left one is to be rotated in clockwise directiln while the right on is to be roated in counter-clockwise direction such that a converging velocity field is made in between the cylinders. but i am not sure how to define the direction because i exactly dont know what (0 0 1) represtns in front of axis. and what if its is (0 0 -1)

I am really confused.

[Bloerb]

origin is the point around which you are rotating. A point alone is however not enough to define a rotation. The axis is the axis around which you are rotating. (0 0 1) means you are rotating around the z axis. For a 2D calculation in the x-y plane this would be the logical choice. The speed at which you are rotating is omega.

Hence your rotation vector is (0 0 1*omega). a positive value of omega now means that you are rotating in a mathematically positive direction (counter-clock-wise). You could either reverse the axis (0 0 -1) to change the direction, or simply define omega as a negative number. Axis is normalized. So (0 0 2) is the same as (0 0 1).

[ShanuNith]

Thanks a lot for quick and elaborate explanation.