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Robbb September 18, 2012 07:49

Parabolic Profile of velocity
How can I introduce a parabolic profile of velocity at the entrance of a straight tube?

wyldckat September 18, 2012 08:44

Greetings Roberto,

Since you're question is so generic, here's a generic answer: ;)

But seriously, what's the context? Is it:
  1. Purely in the mathematical sense?
  2. Purely in the mathematical sense, but in a CFD context/terminology?
  3. In a mathematical software, such as MATLAB or Mathematica?
  4. In a particular CFD software?
  5. In a CAD software? :confused:
  6. In a real life laboratory experiment?
Best regards,

PPS: I've moved this thread to the sub-forum dedicated to FLUENT, given the response on the next post ;)

Robbb September 19, 2012 06:27

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.

rayolau September 20, 2012 07:02

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;
if (y>=S)
F_PROFILE(f,thread,index)=0.55*double log (double (y/0.0016))
But on compiling my UDF I get the error. Any ideas will be appreciated

RodriguezFatz September 20, 2012 10:00


Originally Posted by Robbb (Post 382523)
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.

Robbb October 1, 2012 07:03

I'm trying with this one but it tells me Divergence detected in AMG solver :confused:

#include "udf.h"
#define YMIN 1.2
#define YMAX 1.55
#define UMEAN -0.04150349
#define B 1./7.
#define DELOVRH 0.5

real y, del, h, x[ND_ND], ufree; /* variable declarations */
face_t f;
h = YMAX - YMIN;
del = DELOVRH*h;
ufree = UMEAN*(B+1.);
y = x[1];
if (y <= del)
F_PROFILE(f,t,i) = ufree*pow(y/del,B);
F_PROFILE(f,t,i) = ufree*pow((h-y)/del,B);

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