# UDF for synthetic jet simulation

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 March 18, 2010, 03:55 UDF for synthetic jet simulation #1 New Member   Marcin Join Date: Apr 2009 Posts: 6 Rep Power: 17 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.

March 18, 2010, 04:17
#2
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Sebastian Gatzka
Join Date: Mar 2009
Location: Frankfurt, Germany
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Quote:
 Originally Posted by Chicken where x - radial distance from the center of the diaphragm, w - omega.
I can't imagine what that means.
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March 18, 2010, 04:28
#3
New Member

Marcin
Join Date: Apr 2009
Posts: 6
Rep Power: 17
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
Attached Images
 eq.jpg (3.2 KB, 97 views)

 March 18, 2010, 05:22 #4 Senior Member     Sebastian Gatzka Join Date: Mar 2009 Location: Frankfurt, Germany Posts: 729 Rep Power: 20 What grid are you solving on? 3D, 2D, Axi-Symmetric? __________________ Schrödingers wife: "What did you do to the cat? It's half dead!"

 March 18, 2010, 05:36 #5 New Member   Marcin Join Date: Apr 2009 Posts: 6 Rep Power: 17 I am using 2D (x-y) mesh (and I now realized that it should be axi-symmetric for this velocity profile, am I right?) Chicken

 March 18, 2010, 05:44 #6 Senior Member     Sebastian Gatzka Join Date: Mar 2009 Location: Frankfurt, Germany Posts: 729 Rep Power: 20 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. __________________ Schrödingers wife: "What did you do to the cat? It's half dead!"