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-   -   Rotation in MRF (https://www.cfd-online.com/Forums/fluent/82498-rotation-mrf.html)

 Feitan November 28, 2010 11:24

Rotation in MRF

Hi everybody, I need your help. I'm using an MRF approach, but I have a doubt. My component has to rotate counterclockwise around z axis. My question is: which is the sense of rotation that FLUENT uses? That is, if I set up a rotational speed of 30 rad/s around the z axis (0,0,1), will my component rotate clockwise or counterclokwise? Thank you very much

 kerhart November 28, 2010 14:16

Fluent should be using a right-handed coordinate system, so the rotation should be counter-clockwise using (0,0,1) as the axis. However, if you are unsure, just set the rotation as 30 rad/s and initialize the solution making sure everything is initialized to zero "relative to the adjacent zone". Then (before running the solution at all) view the velocity contours and it should be very clear which direction the region is rotating. If it is wrong, just change it to -30 rad/s and re-initialize. Good luck.

Kevin Erhart, PhD
Research Vice President
Central Technological Corporation
www.centecorp.com

 Feitan November 28, 2010 16:23

Thank you very, very much. I made the test you suggested and now I can confirm that FLUENT uses a right-handed coordinate system, therefore if the rotation axis is (0,0,1) and the rotational velocity is positive, then the component rotates counter-clockwise.

 venkat_aero2007 June 20, 2012 13:41

Contra rotating rotor

Hi ,

I am trying to simulate flow around Contra rotating rotor using mixing plane method. I have some doubt in defining boundary condition on rotor blade.

I defined Front rotor and Second rotor as Stationary wall.
Front rotor is rotating in Counter clock wise direction (according to Right hand thumb rule). So i define the fluid in the Front rotor region as Moving reference frame which rotates about X- axis (1 0 0) at -1800 rpm (negative sign for Counter clockwise direction), Relative to Cell zone:- absolute.

The second rotor rotates in opposite to that of Firs rotor about X-axis (1 0 0) at 1800 rpm (Positive sign for clockwise direction). relative to cell zone: Opposite to front rotor Fluid

When I check the Relative velocity vector, The Direction of the relative vector for the front rotor is along Counter Clockwise direction which is wrong ( it should be in clock wise direction because of the fact that the blade rotates in counter clock wise direction) but the relative velocity vector for the second rotor looks perfect.

Please can someone help me to define the proper boundary condition.