Parabolic Profile of velocity

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 September 18, 2012, 07:49 Parabolic Profile of velocity #1 New Member   Roberto Join Date: Oct 2011 Location: Italy Posts: 17 Rep Power: 8 How can I introduce a parabolic profile of velocity at the entrance of a straight tube?

 September 18, 2012, 08:44 #2 Super Moderator   Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,031 Blog Entries: 39 Rep Power: 110 Greetings Roberto, Since you're question is so generic, here's a generic answer: http://www.google.com/imghp?q=parabolic+profile But seriously, what's the context? Is it: Purely in the mathematical sense? Purely in the mathematical sense, but in a CFD context/terminology? In a mathematical software, such as MATLAB or Mathematica? In a particular CFD software? In a CAD software? In a real life laboratory experiment? Best regards, Bruno PPS: I've moved this thread to the sub-forum dedicated to FLUENT, given the response on the next post __________________ OpenFOAM: FAQ | Getting started Forum: How to get help, to post code/output and forum guide What am I doing/planning: blog/wiki Read this before sending me PM Last edited by wyldckat; September 19, 2012 at 16:54. Reason: see "PPS"

 September 19, 2012, 06:27 #3 New Member   Roberto Join Date: Oct 2011 Location: Italy Posts: 17 Rep Power: 8 Bruno, you've got a good sense of humor . Besides that I'm talking about Fluent 14.0. I need a boundary condition that allows me to introduce a completely developped parabolic profile of velocity of a fluid entering a straight tube (3D). I can either create a very long tube, or create this profile in some way, but I don't know how.

 September 20, 2012, 07:02 #4 New Member   rayolau Join Date: Aug 2012 Posts: 23 Rep Power: 7 Hi, I am working in similar 3D case. At the moment, my macro is this: ____________________________________ #include "udf.h" #define S 0.0016 DEFINE_PROFILE(inlet_x_velocity, thread, index) { real x [ND,ND]; real y; real z; face_t,f; begin_f_loop(f,thread) { F_CENTROID(x,f,thread) y=x[1] z=x[2] if (y>=S) F_PROFILE(f,thread,index)=0.55*double log (double (y/0.0016)) } end_f_loop(f,thread) } _________________________________ But on compiling my UDF I get the error. Any ideas will be appreciated Thanks!

September 20, 2012, 10:00
#5
Senior Member

Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,297
Rep Power: 20
Quote:
 Originally Posted by Robbb I can either create a very long tube, or create this profile in some way, but I don't know how.
I would go for the long tube.

 October 1, 2012, 07:03 #6 New Member   Roberto Join Date: Oct 2011 Location: Italy Posts: 17 Rep Power: 8 I'm trying with this one but it tells me Divergence detected in AMG solver #include "udf.h" #define YMIN 1.2 #define YMAX 1.55 #define UMEAN -0.04150349 #define B 1./7. #define DELOVRH 0.5 DEFINE_PROFILE(x_velocity,t,i) { real y, del, h, x[ND_ND], ufree; /* variable declarations */ face_t f; h = YMAX - YMIN; del = DELOVRH*h; ufree = UMEAN*(B+1.); begin_f_loop(f,t) { F_CENTROID(x,f,t); y = x[1]; if (y <= del) F_PROFILE(f,t,i) = ufree*pow(y/del,B); else F_PROFILE(f,t,i) = ufree*pow((h-y)/del,B); } end_f_loop(f,t) }

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