# Define periodic velocity profile by field function at the inlet

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 June 18, 2015, 13:23 Define periodic velocity profile by field function at the inlet #1 New Member   Xiang Pan Join Date: Jun 2015 Posts: 3 Rep Power: 10 Hello, I am now using STAR-CCM+ to simulation bubble generation in complex microfluidic device. I am considering to use periodic velocity boundary condition at the gas or liquid inlet instead of constant velocity condition. The periodic velocity profile should change with time like a sine function. Could anyone tell me how to define this periodic velocity profile by using field function? Thank you!

 June 19, 2015, 06:30 #2 New Member   Bastian N. Join Date: Jul 2014 Posts: 6 Rep Power: 11 That is quite easily done. First you need to set up a field function including your sinus. E.g. "sin(2*3.1416*\${Time}/0.02)" for a cycle-Time of 0.02 seconds. Than you go to your inlet Boundary, and change under Physics Values the Method of the "Velocity" Property to "Field Function". Now you can choose your just defined field function.

June 23, 2015, 12:03
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Xiang Pan
Join Date: Jun 2015
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Quote:
 Originally Posted by Bust That is quite easily done. First you need to set up a field function including your sinus. E.g. "sin(2*3.1416*\${Time}/0.02)" for a cycle-Time of 0.02 seconds. Than you go to your inlet Boundary, and change under Physics Values the Method of the "Velocity" Property to "Field Function". Now you can choose your just defined field function.
Thank you for your reply. I have successfully applied the field function at the inlet boundary. I also want to know how to apply the same periodic velocity profile at specified position in the geometry by using field function. It will be very grateful if you can give me some advice on this issue. Thank you.

 June 25, 2015, 08:44 #4 New Member   Bastian N. Join Date: Jul 2014 Posts: 6 Rep Power: 11 As far as I know you can not apply a velocity constraint just somewhere inside the fluid domain. Can you give some more informations about your case, because I can not really imagine why you should want to predefine the velocity profile inside the flow from a physical point of view. Maybe we can then find a little workaround for your problem.

 June 24, 2017, 04:07 #5 New Member   Dhanam Koilraj Join Date: Jan 2017 Posts: 1 Rep Power: 0 How do you set up a field function ? Is it using udf ?

 Tags field function, velocity bc