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Haris Maharana January 16, 2001 07:33

applying boundary condition on rotating wall
My CFD problem is related to the relative rotation between two parallel no-slip walls (with fluid in-between) at a certain horizontal distance. I will call them as "left wall" and "right wall".

The "left wall" is stationary and the "right wall" is rotating at a certain speed. I am applying the following boundary conditions on these two walls :

1) Left wall : no-slip, omega = 0 ;

2) Right wall : no-slip, omega = some finite value.

Will these boundary conditions take care of the non-rotational effect of the "left wall" and "rotational" effect of the right wall?

If not, can anybody suggest the right way to apply the boundary conditions on these walls?

N.B. : Application of "sliding mesh theory with event module" will to help in this problem.

John C. Chien January 16, 2001 08:53

Re: applying boundary condition on rotating wall
(1). I find it hard to believe that there are non-rotational effect as well as rotational effect. (2). I have not used the code myself. But you shouldn't be worrying about the effect when setting the boundary conditions. (3). If the solution is not responding to the boundary conditions, then it is likely that you are not following the instructions correctly. (4). Well, in your simple problem, you can use either the fixed stationary reference frame (coordinate system) as you just did, or the moving (rotating) reference frame attached to the rotating wall. One is enough. (5). You will have to read your tutorial samples to find out how to set the boundary conditions properly. Each code has its own way of setting the conditions, especially when using the moving reference frame. (6). By the way, what are the non-rotational and rotational effects you are looking for? I have worked in the turbomachinery field for many years, but I have never heard of such effects mentioned before. But anyway, each company always has its own way of defining thing differently. (if you have a rotating wall, the flow field will be rotating everywhere, except fluid particles on the stationary wall. But if you use wall function treatment through turbulence model, you will not see these stationary fluid particles, because then the whole flow field will be all rotating. the fluid layer next to the stationary wall is not computed explicitly when wall function is used.)

J. Y. Luo January 16, 2001 13:03

Re: applying boundary condition on rotating wall
If you are simulating flow between two parallel plates (walls), then the only thing you need to do is specifying the wall boundary conditions as you described. Then through diffusion effect, the velocities will be known to the inside flow.

However, if you have baffles attached to the walls (such as mixing vessel), then you have to use either multiple rotating frames approach or sliding mesh to deal with the problem.

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