# Outlet Pressure-flow coupled boundary condition (Windkessel)

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 November 16, 2010, 18:45 Outlet Pressure-flow coupled boundary condition (Windkessel) #1 New Member   CFDFSI Join Date: Dec 2009 Posts: 4 Rep Power: 9 Hi, I'm trying to apply a windkessel type boundary condition at the outlet, which is of the form: P(t) + k*P'(t) = Q(t), where k is a known constant To do this, I model the outlet as a 'pressure-outlet' and use a UDF to impose P(t) on the outlet faces. To calculate P(t), I approximate P'(t) by [P(t) - P(t-1)]/delta_t, and arrive at the closed form expression P(t) = Function[P(t-1), Q(t), k, delta_t] My question is: how do I specify this equation in the UDF ? At present, I'm using the DEFINE_PROFILE(pressure, t, i) macro, calculating Q(t) by Code: ```density = 100; sumFlow = 0; face_t f; begin_f_loop(f, t) { sumFlow = sumFlow + F_FLUX(f,t); } end_f_loop(f, t) sumFlow = sumFlow/density;``` Now, what is the best way to find P(t-1) on all the faces of the outlet ? Is there a macro like F_P_M1(f,t) ?

 October 12, 2011, 10:01 #2 New Member   Join Date: Sep 2009 Posts: 9 Rep Power: 10 I am also facing the same problem. Does anyone has answer for this. Also since Q is evaluated at current time step. I need to iterate to get p. How should I do the iteration using UDF? Thanks a lot

 December 11, 2015, 23:48 #3 Member     Pranjal Singh Join Date: Sep 2015 Posts: 34 Rep Power: 4 I'm also stuck on this. I made UDM for storing P(t-1) and initialised it. So, it should work but in the results, I see that the compliance phenomenon isn't observed. I've modelled wall material as elastic. Does it need to be hyperelastic or something to get FSI coupling behavior?

 July 21, 2017, 12:30 #4 Member   Ali.E Join Date: Sep 2010 Location: Lisboa Posts: 83 Rep Power: 9 Dear all, did you manage the problem? I have aslo the same issue, I need previous time step preesure on the wall, please let me know if you found any solutions

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Sastry FLUENT 4 February 19, 2011 02:33 Mohsin FLUENT 1 April 30, 2010 10:36 Pankaj CFX 9 November 23, 2009 05:05 Matt Umbel Main CFD Forum 0 January 11, 2002 11:06 HB &DS CFX 0 January 9, 2000 14:19

All times are GMT -4. The time now is 19:20.

 Contact Us - CFD Online - Privacy Statement - Top