# Oscillatory flow in a pipe

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 June 18, 2009, 05:13 Oscillatory flow in a pipe #1 New Member   thomas Join Date: Jun 2009 Location: Edinburgh Posts: 12 Rep Power: 9 Hi, I would like to simulate an oscillatory flow crossing a pipe. I wonder if I have to use periodic boudaries condition (inlet/outlet) or not? Also can I use a user fonction to define my flow inlet (like: sin(cst*\$Time) )? Thanks in advance. Tom

 June 18, 2009, 08:10 #2 Senior Member   Aroon Join Date: Apr 2009 Location: Racine WI Posts: 148 Rep Power: 9 Hello Thomas, I have used a time varying inlet velocity before using the sine function defined as a separate field function and calling the field function as the BC. However in my case, the velocity was always positive and I imposed this velocity as an inlet BC. My function was of the form V = V0 (2 - sin(w*t)) It worked well. However I have not tried a case with a function where teh flow could go negative, like V = V0 sin(w*t).

 June 18, 2009, 09:00 #3 New Member   thomas Join Date: Jun 2009 Location: Edinburgh Posts: 12 Rep Power: 9 Many thanks for your answer. I am using a User field fonction now. Yes in my case the velocity can be negative. So may be I think I have to use periodic BC but I don't really understand how periodic BC work. Someone could give me information regarding Periodic BC. Thanks.

 June 18, 2009, 10:11 #4 Senior Member   Aroon Join Date: Apr 2009 Location: Racine WI Posts: 148 Rep Power: 9 Hello Tom, To use periodic BC you have to select the two boundaries that are periodic and then define an interface between them. This interface then has to be defined as Periodic and Fully Developed. But using the periodic BC in STAR CCM+ gives you periodicity in space, not in time.

 June 19, 2009, 05:05 #5 New Member   thomas Join Date: Jun 2009 Location: Edinburgh Posts: 12 Rep Power: 9 Hello Aroon, Many thanks for these information. In fact, for me periodicity in space is not really clear. I don't understand very well of what it consists. Thanks.

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