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Old   March 18, 2010, 04:55
Default UDF for synthetic jet simulation
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Marcin
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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.

Chicken

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.
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Old   March 18, 2010, 05:17
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Sebastian Gatzka
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Quote:
Originally Posted by Chicken View Post
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.
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Old   March 18, 2010, 05:28
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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)

where:
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).

chicken
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Old   March 18, 2010, 06:22
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What grid are you solving on?
3D, 2D, Axi-Symmetric?
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Old   March 18, 2010, 06:36
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I am using 2D (x-y) mesh (and I now realized that it should be axi-symmetric for this velocity profile, am I right?)

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Old   March 18, 2010, 06:44
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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.
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