CFD Online Discussion Forums

CFD Online Discussion Forums (
-   Fluent UDF and Scheme Programming (
-   -   UDF for synthetic jet simulation (

Chicken March 18, 2010 04:55

UDF for synthetic jet simulation
Hi everybody.
I'm a student and I'm working on synthetic jet 2D simulation (closed cavity with membrane on one side and an orifice face to the membrane). I identified the membrane as a wall and the external domain as a pressure-outlet. I am trying to simulate vortex creation at the orifice exit. I am begginer in UDF's, for the first simulation I used DEFINE_PROFILE for membrane (identified as a velocity inlet) but with this macro I can't observe membrane's displacement, so I tried to use DEFINE_GEOM and DEFINE_GRID_MOTION and here comes my problem. Membrane's velocity along Y axis is given by equation:

vel [1] = 0.0603*(1. - (6400.*x*x) + (12800.*x*x)*((double)log((double)80.*x)))*cos(w * time);

where x - radial distance from the center of the diaphragm, w - omega. Could someone help me and tell me how can I put this velocity equation into DEFINE_GEOM or DEFINE_GRID_MOTION udf? Please take into account that I'm a student. I tried to modify UDF's from tutorial but with no success :( Thank you very much in advance for any advice.


p.s. I can not contact with FLUENT help because I am working on computer at the University and I don't have license for my own.

sega March 18, 2010 05:17


Originally Posted by Chicken (Post 250538)
where x - radial distance from the center of the diaphragm, w - omega.

I can't imagine what that means.
Give us some more details about your domain.

Chicken March 18, 2010 05:28

1 Attachment(s)
Sega thx for reply.
I will try to explain, on the attached picture equation for membrane's velocity is given (I am using this equation, found it in paper "Piezoelectric Actuators as Synthetic Jets" POORNA MANE, KARLA MOSSI, ALI ROSTAMI, ROBERT BRYANT AND NICOLAS CASTRO)

delta_c - peak-to-peak membrane's displacement;
Dd - membrane diameter and r - radial distance from the center of the diaphragm (in my case radius is along X axis).


sega March 18, 2010 06:22

What grid are you solving on?
3D, 2D, Axi-Symmetric?

Chicken March 18, 2010 06:36

I am using 2D (x-y) mesh (and I now realized that it should be axi-symmetric for this velocity profile, am I right?)


sega March 18, 2010 06:44

I'm not sure, it depends on your problem.

For the realization of the equation you will simply have to use the mesh coordinate in radial direction.

You should be able to look the appropriate variable in the UDF manual.

All times are GMT -4. The time now is 17:05.