Parabolic Profile of velocity

Robbb · September 18, 2012, 08:49

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

wyldckat · September 18, 2012, 09:44

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

Robbb · September 19, 2012, 07:27

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, 08:02

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;
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!

RodriguezFatz · September 20, 2012, 11:00

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.

Robbb · October 1, 2012, 08:03

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)
}

September 18, 2012, 08:49	Parabolic Profile of velocity	#1
Robbb New Member Roberto Join Date: Oct 2011 Location: Italy Posts: 17 Rep Power: 15	How can I introduce a parabolic profile of velocity at the entrance of a straight tube?

September 18, 2012, 09:44		#2
wyldckat Retired Super Moderator Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,982 Blog Entries: 45 Rep Power: 128	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 Read this before sending me PM Last edited by wyldckat; September 19, 2012 at 17:54. Reason: see "PPS"

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September 19, 2012, 07:27		#3
Robbb New Member Roberto Join Date: Oct 2011 Location: Italy Posts: 17 Rep Power: 15	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, 08:02		#4
rayolau New Member rayolau Join Date: Aug 2012 Posts: 23 Rep Power: 14	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!

October 1, 2012, 08:03		#6
Robbb New Member Roberto Join Date: Oct 2011 Location: Italy Posts: 17 Rep Power: 15	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 = DELOVRHh; 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) = ufreepow(y/del,B); else F_PROFILE(f,t,i) = ufree*pow((h-y)/del,B); } end_f_loop(f,t) }