# 1/7th power law

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

 February 29, 2012, 17:01 1/7th power law #1 New Member   Join Date: Dec 2011 Posts: 17 Rep Power: 7 I am trying to work out static pressure distribution across an orifice. i have plotted it and noticed that since the upstream pipe length is not long enough the flow is not becoming fully developed(turbulent). I looked at how it was meant to be modelled and it says inlet boundary condition with 1/7th power-law was used. i know this has something to do with User defined functions which i am unfamiliar with. Do i have to do some programming or something? or is it a setting within fluent. thank you for any help.

 February 29, 2012, 20:51 #2 New Member   Join Date: Dec 2011 Posts: 17 Rep Power: 7 I have found a 1/7th power law but when i interpret i get the following error: line 9: parse error. I think it means the line DEFINE_PROFILE(x_velocity,t,i) but i dont know why that is since i copied and pasted it from the UDF manual. i have changed the value for YMAX and UMEAN. Any help would be gladly appreciated. Thank you. /*#include "udf.h"*/ #define YMIN 0.0 /* constants */ #define YMAX 0.05 #define UMEAN 20.0 #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) }

 March 1, 2012, 01:38 #3 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 996 Rep Power: 17 Hi, uncomment the first line #include uds.h. Take in mind that this udf will work for 2d axisimmetric problem. Daniele

 March 1, 2012, 14:09 #4 New Member   Join Date: Dec 2011 Posts: 17 Rep Power: 7 Thanks for the reply Danielle. It worked fine. Since the model is axisymetric, does it mean YMAX is the actual diameter or half of it as it is modelled. Thank you

 March 1, 2012, 20:03 Axial velocity with parabolic profile #5 New Member   Join Date: Dec 2011 Posts: 17 Rep Power: 7 Is there a udf that i can use to specify an inlet boundary condition for laminar flow that will give axial velocity with parabolic profile. Thanks.

March 2, 2012, 07:33
#6
Senior Member

Daniele
Join Date: Oct 2010
Location: Italy
Posts: 996
Rep Power: 17
Quote:
 Originally Posted by Gamb1t Thanks for the reply Danielle. It worked fine. Since the model is axisymetric, does it mean YMAX is the actual diameter or half of it as it is modelled. Thank you
Hi, YMAX refers to your axisymmetric grid so it's half diameter.

Daniele

 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 John FLUENT 16 September 12, 2015 06:18 hellouch FLUENT 3 April 21, 2009 03:03 Eric CFX 3 January 10, 2007 08:16 Francesca Chiusa FLUENT 1 November 3, 2006 15:30 Poly FLUENT 0 March 24, 2005 16:12

All times are GMT -4. The time now is 20:02.