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UDF inlet velocity profile mismatch with Fluent |
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February 16, 2010, 15:11 |
UDF inlet velocity profile mismatch with Fluent
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#1 |
New Member
Join Date: Feb 2010
Posts: 1
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I am prescribing a velocity profile at the inlet of my mesh. Fluent compiles the c file fine and the solution does converge. However, the velocity profile that I am inputting is a parabola and Fluent does not plot the correct shape of my profile at the inlet. My UDF code is show below. My y coordinates start at zero and goes to 0.0093 m.
Any ideas on why Fluent is not interpreting the correct velocity profile would be appreciated. #include "udf.h" #include "mem.h" /** Parameter Constants **/ #define wallspeed 7.0711 #define finalheight 0.0093 #define height 0.001 /***************** Inlet Velocity Profile in Slot *****************/ DEFINE_PROFILE(inlet_velocity_profile,thread,posit ion) { real x[ND_ND]; real y; face_t f; begin_f_loop(f,thread) { F_CENTROID(x,f,thread); y = fabs(x[1]); F_PROFILE(f,thread,position) = wallspeed*(((6/(finalheight*finalheight))*((1/2)-(height/finalheight))*((y*y)-(finalheight*y)))-(y/finalheight)+1); } end_f_loop(f,thread) } |
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February 22, 2010, 15:17 |
profile in the velocity inlet
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#2 |
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Elahe
Join Date: Oct 2009
Posts: 21
Rep Power: 16 |
hi...
did you solve your problem, i have this problem,too. thanks, elahe |
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February 23, 2010, 02:01 |
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#3 |
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Amol Ramteke
Join Date: May 2009
Location: Kolkata
Posts: 30
Rep Power: 17 |
Ohhhh,
There is problem in your geometry creation. Remember the velocity profile given for pipe, y= something something... for e.g the pipe is of diameter 1m on y axis. you should construct it as (y=+0.5 and y=-0.5 and centre of pipe should be at "zero") either you can make changes in udf but i feel that is tidious(not that much). Amol |
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February 24, 2010, 04:43 |
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#4 |
New Member
Elahe
Join Date: Oct 2009
Posts: 21
Rep Power: 16 |
hi Goldsstean
thanks for your attention it's a bit odd, my case is a canal and i want to make wave in that. 'y' in my case is calculate from the bottom of canal , is different with pipe,ya? do you try yoursef? i try your idea.... best elahe |
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February 24, 2010, 04:48 |
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#5 |
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Amol Ramteke
Join Date: May 2009
Location: Kolkata
Posts: 30
Rep Power: 17 |
Could you please explain your problem in detail.
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February 24, 2010, 07:23 |
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#6 |
New Member
Elahe
Join Date: Oct 2009
Posts: 21
Rep Power: 16 |
i model a canal with 20 m lenght and 15 m height in 2d fluent.
i wanna generate wave in canal and i hook a udf file that velocity time varing was defined in it for x and y direction. wave is generated correctly but velocity profile plot is not correct and do not match with velocity countor. it seems velocity countor is right and match with theory but profile is wrong. i set velocity inlet in the left border of canal. and in plot menu >xy plot> i write a file of velocity in this boundary. is my way right or not? thanks in advance elahe |
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February 10, 2012, 05:06 |
how do give parabolic inlet velocity
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#7 |
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saravanan
Join Date: Oct 2011
Posts: 2
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how do give parabolic inlet velocity profile for supersonic nozzle
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February 13, 2012, 04:22 |
udf for velocity profile
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#8 |
New Member
maryam ghadiri
Join Date: Feb 2012
Posts: 1
Rep Power: 0 |
dear all, i am new in fluent simulation. I write a udf file to define a terrain for my case. I use log law for velocity but I face to this massage: " number error floatingpoint error" .
would you please help me. this is my udf file: #include "udf.h" DEFINE_PROFILE(log_velocity,thread,position) { real x[ND_ND]; real y; face_t f; begin_f_loop(f,thread) { F_CENTROID(x,f,thread); y = x[1]; F_PROFILE(f,thread,position) = 5*log(y/0.4)/log(10/0.4); } end_f_loop(f,thread) } Last edited by maryamgh; February 13, 2012 at 21:01. |
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February 14, 2012, 01:50 |
UDF for density variation
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#9 |
New Member
deepak
Join Date: Feb 2011
Posts: 8
Rep Power: 15 |
Please help me in making a UDF for following condition=
Variable density was defined in the liquid state as q = ql/[b(T - Tl) + 1] for 30C < T < 100 C, where q = 760 kg/m3, Tl = 30 C, and b = 0.0005 , with linearly varying density in the ‘‘mushy” state, from 870 kg/m3 at 28 C to 760 kg/m3 at 30 C. |
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June 21, 2013, 14:42 |
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#10 |
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Mahboobe Mahdavi
Join Date: Mar 2013
Posts: 22
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June 24, 2013, 06:10 |
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#11 |
New Member
Ravindra
Join Date: May 2013
Posts: 5
Rep Power: 13 |
Do u get the solution to your problem? I am also getting the same problem but in giving the transient temperature profile.
Any help would be appreciated. |
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October 5, 2016, 04:24 |
open channel problem
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#12 |
Member
muhamed
Join Date: Jun 2013
Posts: 66
Rep Power: 13 |
Hi everybody,
I have a problem with the wind pressure distribution on a building. As you can see from the attached picture (Picture 1), which I downloaded it from the internet, the pressure at the lower part of the building is much less than that at the upper part and this is expected to be happened because the wind velocity near the ground is much less than that at the top. The problem I faced is that the wind pressure be the same along the height of the building (Picture 2). Does anyone can help me? |
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November 23, 2016, 22:01 |
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#13 |
New Member
Yousef
Join Date: Dec 2015
Posts: 14
Rep Power: 10 |
Hi Muhamed,
You need to define a velocity profile the varies with height at the inlet using a UDF. I would also suggest that you refine the mesh near the building. By the way, do you happen to know the source for Picture 1? Thanks Y.A.Z |
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November 24, 2016, 04:37 |
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#14 | |
Member
muhamed
Join Date: Jun 2013
Posts: 66
Rep Power: 13 |
Quote:
Do you have a UDF for inlet velocity profile in an open channel? I couldn't find it in the INTERNET and I don't know how to write the UDF that I need. Regarding Picture 1, as I remember, I took it from an article about air velocity distribution on a building. |
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November 25, 2016, 03:32 |
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#15 |
Senior Member
Join Date: Mar 2015
Posts: 892
Rep Power: 18 |
Here is a UDF for defining a velocity profile along a boundary for wind modelling around buildings: http://www.cfd-online.com/Forums/flu...nd-height.html
Edit the following equation to your inlet velocity profile (z is the z-direction height in their UDF): Code:
F_PROFILE(f, thread, position) = 24.9 *pow(z,0.27); |
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November 25, 2016, 06:45 |
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#16 | |
Member
muhamed
Join Date: Jun 2013
Posts: 66
Rep Power: 13 |
Quote:
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