Pb velocity formulation
 

Hello everyone,

I am working on Fluent 12.1 and I am facing issues with the velocity formulation. First let me present you my configuration:

I have a fan composed with a tuyere at the inlet, 8 rotor blades and an axe placed at the center of the fan. The problem is that the entire fan is rotating with a radius of 10 mms and at a speed x in regard to the absolute frame. But inside this fan the axe, and therefore the rotor which is attached to, is rotating at a speed equals to 6*x in regard to the absolute frame (fyi thanks to a cog-wheel). I am working with an incompressible assumption and therefore I have the choice between "absolute" and "relative" in the velocity formulation (module "general"). I also defined two fluids, one called "fluid-mrf" for the volume corresponding to the rotor, and the rest is simply called "Fluid".

My questions are numerous, and if someone has an answer for at least one it would be very helpful :) :

- In that configuration, is it better to put in Fluent that the fluid is not rotating (cell zone conditions -> Fluid -> Motion Type -> stationary) and that the different walls (tuyere, axe, rotor) are moving at different rotations (in boundary conditions) or that the 2 fluids must be defined in two different rotating frames ?
- If two rotating frames must be defined, is it better to say that the walls are stationnary (in boundary conditions->edit->wall motion) or that they are moving walls with a speed relative to the adjacent cell zones equals to 0 ?

- In either case, how the velocity formulation must be changed to ?

- I have doubts concerning the display of the relative velocity : in regard to which frame is it displayed ? Is it regard to the one where the fluid being observed is defined, or to another frame ?

-Finally, what is the code you have to put in a journal file to change the value of the velocity formulation ? I have searched in all the \define paths but I couldn't find it.


Thanks a lot for the answers, and sorry for the long post but I am not used to deal with multiple rotationnal speeds !

Thomas