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Leigh July 7, 2006 05:28

Vibrating Wall
Hello all,

I have a nozzle that has an constant inlet velocity and a inner vibrating wall. For the vibrating wall I have used a UDF and assigned it in the momentum section of the boundary conditions. When analysing the moniter I assigned to the wall, it shows that the wall IS vibrating as I wish it to. The problem is this is not shown when I contour plot the nozzle, i am expecting to see both pressure change and velocity change caused by the wall vibrating back and forwards around the wall. I have used the vibrating udf for an inlet velocity boundary condition in a previous model and it worked fine,

Any ideas..........?

Thanks in advance, Leigh

Abdula Brinza July 11, 2006 02:37

Re: Vibrating Wall
If vibrating surface type is WALL, FLUENT allows it to move in-plane only, that is drops velocity components normal to boundary. Also check length scale - do you resolve boundary layer?

Leigh July 11, 2006 06:57

Re: Vibrating Wall
Thanks for your reply.

In my model I only want the wall to vibrate normal to the boundary (ie left and right in a 2D plane), so I think that is ok. The scale of the model is correct, it is very small, ie the virbrating wall is of length around 17E-06m. Also what do you mean by resolving the boundary layer?

Ive done alot of browsing the manual and think maybe I need a dynamic mesh to model the vibrating wall.

Any further thoughts?

Luca Cavagna July 11, 2006 08:49

Re: Vibrating Wall
Yes you need to use the dynamic mesh because Fluent cannot account for normal velocity in the wall bc (only tangential). Luca

Leigh July 13, 2006 03:33

Re: Vibrating Wall

Thanks for the reply, I have never used a dynamic mesh before. I have had a look through the manual and the tutorial but I am not clear in what I am supposed to do. My model is a simple nozzle that has a vibrating wall that is designed to nebulise the fluid. I would like to see if there is any cavitation around this wall.

Any help or pointers on dynamic meshes??

Thanks, Leigh

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