# parabolic velocity by groovy bc

 Register Blogs Members List Search Today's Posts Mark Forums Read

May 14, 2014, 05:55
parabolic velocity by groovy bc
#1
Senior Member

Ali reza
Join Date: Mar 2014
Posts: 103
Rep Power: 5
hi
I am going to have parabolic velocity inlet and I have defined it in a pipe which it diameter is 4mm and flow is laminar and this is the definition of fully developed flow in a pipe

u z = u max (1 −r2/R2) and this is my definition
Code:
```   {
inlet
{
type            groovyBC;
refValue        uniform (0 0 0);
valueFraction   uniform 1;
value           uniform (0 0 0);
valueExpression "vector(Umax*(1-(sqr(r)/sqr(0.004))),0,0)";
fractionExpression "1";
evaluateDuringConstruction 0;
variables       "r=sqrt(pow(pos().y,2)+pow(pos().z,2));Umax=0.07;";
timelines       ();
lookuptables    ();
}```
but I am not sure about defining "r" as a radius in this way because the coordinate is changing and using "sqrt((z**2)+(y**2))" is not true for everywhere,Am I right?
and the other problem is I have got this velocity profile instead of parabolic one.
thanks guys
Attached Images
 pic3.jpg (18.3 KB, 40 views) pic2.PNG (9.3 KB, 32 views)

May 14, 2014, 09:30
#2
Assistant Moderator

Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,997
Rep Power: 42
Quote:
 Originally Posted by 1988 hi I am going to have parabolic velocity inlet and I have defined it in a pipe which it diameter is 4mm and flow is laminar and this is the definition of fully developed flow in a pipe u z = u max (1 −r2/R2) and this is my definition Code: ``` { inlet { type groovyBC; refValue uniform (0 0 0); refGradient uniform (0 0 0); valueFraction uniform 1; value uniform (0 0 0); valueExpression "vector(Umax*(1-(sqr(r)/sqr(0.004))),0,0)"; gradientExpression "vector(0,0,0)"; fractionExpression "1"; evaluateDuringConstruction 0; variables "r=sqrt(pow(pos().y,2)+pow(pos().z,2));Umax=0.07;"; timelines (); lookuptables (); }``` but I am not sure about defining "r" as a radius in this way because the coordinate is changing and using "sqrt((z**2)+(y**2))" is not true for everywhere,Am I right? and the other problem is I have got this velocity profile instead of parabolic one. thanks guys
The equation for r looks alright to me assuming that the center of your inlet is (someX,0,0): centered on the x-axis

What do you mean with "coordinate is changing"? Even if your mesh is moving r is OK. r is a basically a field of values: one for every face of the patch. So it calcs r for every face separately (was this your concern)?
__________________
Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request

 May 14, 2014, 12:10 #3 Senior Member   Ali reza Join Date: Mar 2014 Posts: 103 Rep Power: 5 yes I got what you explained and thats helpful.thanks for your answer however do you have any idea about the wrong velocity pattern which I have got at inlet ? it suppose to be parabolic but it is something else

May 14, 2014, 12:43
#4
Assistant Moderator

Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,997
Rep Power: 42
Quote:
 Originally Posted by 1988 yes I got what you explained and thats helpful.thanks for your answer however do you have any idea about the wrong velocity pattern which I have got at inlet ? it suppose to be parabolic but it is something else
What I don't understand about this diagram: what is the distance on the bottom? Because for instance if it is y or z then it should go from -0.004 to 0.004. If it is the 3 of the points it should go from 0 to 0.004.
__________________
Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request

 May 14, 2014, 13:10 #5 Senior Member   Ali reza Join Date: Mar 2014 Posts: 103 Rep Power: 5 coordinates are (3 points of circle at velocity inlet) (-0.008,0,0.020) (-0.008,0.004,0.024) (-0.008,0,0.028) it means that radius=0.004

May 14, 2014, 14:12
#6
Assistant Moderator

Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,997
Rep Power: 42
Quote:
 Originally Posted by 1988 coordinates are (3 points of circle at velocity inlet) (-0.008,0,0.020) (-0.008,0.004,0.024) (-0.008,0,0.028) it means that radius=0.004
I don't understand what these 3 coordinates are saying (apart from being in the x=-0.008-plane). Please reread the above comment "The equation for r looks alright to me assuming that the center of your inlet is (someX,0,0): centered on the x-axis". Your example doesn't convince mit at all that this is the case.

Please check whether this is the case specify what "distance" in your diagram means.

I will NOT answer anything that arrives in the next couple of hours to give you time to properly think it through
__________________
Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request

 May 15, 2014, 02:37 #7 New Member   Join Date: May 2014 Posts: 7 Rep Power: 5 oh I got it you are right and I find the solution thanks a lot

 May 15, 2014, 02:55 #8 Senior Member   Ali reza Join Date: Mar 2014 Posts: 103 Rep Power: 5 thanks it seems that it was other user's problem too however thanks for your protect

 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 saaghi Main CFD Forum 8 February 7, 2014 09:06 ofslcm OpenFOAM Programming & Development 12 February 5, 2014 01:30 Angeline FLUENT 0 January 27, 2011 08:49 zumaqiong FLUENT 2 February 22, 2010 10:46 Rashad FLUENT 2 February 29, 2008 03:36

All times are GMT -4. The time now is 13:13.