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

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?

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?

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

Hello,

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