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-   -   (ask) how to create UDF for inlet velocity profile (https://www.cfd-online.com/Forums/fluent-udf/86275-ask-how-create-udf-inlet-velocity-profile.html)

 armanrazy May 29, 2013 06:04

salam

 yunusrulz August 14, 2013 13:05

Defining TOP HAT VELOCITY profile

I want to define a top hat velocity profile at my inlet. I dont know the code to define top hat velocity profile. does any body know it. Please answer.

 Ammofreak January 14, 2014 05:58

Velocity inlet UDF in fluent

hi guys,

I want to use a user defined function for velocity inlet for following conditions:

v_x = (2/3)*z for z = 0 to 30
v_x = 20 for z = 30 to 70
v_x = (200/3)-(2/3)*z for z = 70 to 100

It is for 3D compressor cascade inlet. I do not know how to write such functions.
Can anyone help me?

 Sherlock_1812 July 9, 2014 14:01

Hello,

I have a 2D axisymmetric geometry where I want to impose a non uniform velocity field in the fluid region (not a boundary, but the internal field). I have the coordinates and the axial and radial velocity components from a previous simulation.

How do I go about importing this into the current case. Also is there a better way to store the velocity value other than File -> Export?

 roopesh99 January 12, 2016 11:03

Periodic BC DDPM, UDF

Dear Friend,
I am using, DDPM simulation using ANSYS 14.5, for a simple system. I used inlet as periodic and outlet as shadow in ANSYS for making it periodic but after making periodic I have no control on the inlet (I am unable to specify mass flow rate inlet), it is showing option to specify pressure gradient.

 Keyu April 25, 2016 19:41

UDF for inlet y velocity 2D

Hi,

I have seen and used UDFs for the inlet x velocity, but what do I do to make a UDF for inlet y velocity.

Here is the UDF that I used for inlet x velocity.
[
#include "udf.h"
#define umean 10.0
#define R 0.0005
DEFINE_PROFILE(inlet-x-velocity,t,i)
{
real x[ND_ND];
real y;
face_t f;
begin_f_loop(f,t)
{
F_CENTROID(x,f,t);
y = x[1];
F_PROFILE(f,t,i) = (3./2.)*umean*(1-pow((y-R)/R,2));
}
end_f_loop(f,t)
}
]

I tried replacing x with y and vice versa to hopefully get the y-direction velocity, but unsuccessful.

Any suggestions here will be useful.

Thanks,
Keyu

 Bruno Machado April 26, 2016 05:58

Quote:
 Originally Posted by Keyu (Post 596670) Hi, I have seen and used UDFs for the inlet x velocity, but what do I do to make a UDF for inlet y velocity. Here is the UDF that I used for inlet x velocity. [ #include "udf.h" #define umean 10.0 #define R 0.0005 DEFINE_PROFILE(inlet-x-velocity,t,i) { real x[ND_ND]; real y; face_t f; begin_f_loop(f,t) { F_CENTROID(x,f,t); y = x[1]; F_PROFILE(f,t,i) = (3./2.)*umean*(1-pow((y-R)/R,2)); } end_f_loop(f,t) } ] I tried replacing x with y and vice versa to hopefully get the y-direction velocity, but unsuccessful. Any suggestions here will be useful. Thanks, Keyu
This line varies the position along the X, Y, Z axis (0,1,2 respectively).

y = x[1];

If you want a velocity profile normal to the Y direction, you need to use the variation of the position in the X direction if 2D and X and/or Z direction if 3D.

 roopesh99 April 27, 2016 12:09

Dear
u r right..

 mmunige October 24, 2016 05:51

UDF for inlet temperature

Dear all

I have following UDF for inlet temperature, untill 1300s it takes correct values according to equation, but after 1300s values are higher and not accorrding to equation, like at 1301s it should have value of 405C but in simulation inlet temperature is 621C. I could not find the error in my UDF after lot of try. please check this and guide me
#include"udf.h"

{

face_t f;

{

real t = RP_Get_Real("flow-time");

if (t <=1300.0 )

{

}

else if (1300.0 < t && t <= 1500.0 )

{

F_PROFILE(f,thread,position)= -1.04289036878969*pow(10,-10)*pow(t,6.0)+ 8.86126436853789*pow(10,-7)*pow(t,5.0)-3.13621260398811*pow(10,-3)*pow(t,4.0)+5.91804640375908*pow(t,3.0)-6.27969461279651*pow(10,3)*pow(t,2.0)+ 3.55273415252714*pow(10,6)*t - 8.37223405676245*pow(10,8);
}
else
{

F_PROFILE(f,thread,position) = -9.51538261322402*pow(10,-23)*pow(t,6) + 8.26192751387975*pow(10,-18)*pow(t,5)-2.85237398505875*pow(10,-13)*pow(t,4)+4.97518353700886*pow(10,-9)*pow(t,3)-4.58733775886876*pow(10,-5)*pow(t,2)+ 2.10251137071757*pow(10,-1)*t +3.57252192344954*pow(10,2);

}

}

}

 pakk October 24, 2016 11:36

Code:

`else if (1300.0 < t && t <= 1500.0 )`
should be

Code:

`else if ((1300.0 < t) && (t <= 1500.0 ))`

Sinus velocity

Hello
I have a question
How write( V=Asinwt) in fluent(udf)
Thank you

 pakk January 25, 2017 03:47

If you use this UDF:

Code:

`Message("V=Asinwt");`
The text you requested will be written in Fluent.

This is almost surely not what you want, but I can not guess what you really want. You should explain better what you want the UDF to do.

Edit: let me be a little bit more helpful, after drinking coffee.

If A, w and t are defined variables, and you want to put the result in V, the way to put that in a UDF is:
Code:

` V = A*sin(w*t);`
But there is a lot that you have to put around this code (to define A, w, and t, and tell the computer what to do with V), and that depends on what you want to do with it.

Sinus velocity

Thank you for the answers you have given me. I want to examine the impact of heat transfer in an oscillating jet, for sinusoidal input speed jet was
u = Asinwt
The A (Initial velocity), w (period), t (time)
But I do not know how to code the program is written udf

 pakk January 26, 2017 03:56

Look for a UDF that does something similar, and change it.
There are UDFs mentioned in the messages above that do something similar... Read them!

 hemmt January 28, 2017 13:11

how to use data from .csv file as inlet boundry condition

hello every one
i have data file generated from matlab program which contains fluctuating velocity for atmospheric boundary layer
so please guide me how can i use this file as inlet boundary condition

thanks and regards

 saifmasood January 30, 2017 05:08

2 Attachment(s)
Quote:
 Originally Posted by Amir (Post 334682) Dear Naimah, It depends, e.g. if you want to have pressure or velocity in a specified point, you can use "solve->monitor->surface ...."; if you didn't activate it before iteration, you have to write a simple journal file for this purpose. For extracting data of cross-sections; firstly you need to generate these cross-sections in "surface->quadratic or plane" then you can export desired data to other post processors in "file->export". But if you want to export these data for successive time steps; you have to choices: 1) there is such capability in ver. 13 in "file-> export" I think. 2) you can write a journal file to do what you want during iteration. Bests,
Hi... Amir ...I had carried a simulation on shuttlecock. but my contours for radial velocity and tangential velocity are odd. I had attached the files can u help me with this.
Attachment 53614

Attachment 53615

 Thomas_henderson February 11, 2017 10:54

Error message : output pipe has been closed

Hi there,

I have tried to implement this UDF in ansys fluent however it is resulting in an error stating :

" output pipe has been closed "

Any ideas why this might be?

 pakk February 13, 2017 05:29

Which one is "this UDF"?

 Thomas_henderson February 13, 2017 05:50

Udf

Quote:
 Originally Posted by pakk (Post 636898) Which one is "this UDF"?
#include "udf.h"

{
face_t f;
real t = CURRENT_TIME;
real vel;

vel= 0.2+0.1*sin(t);

{

}

 Thomas_henderson February 14, 2017 12:45

Syntax error

There is a syntax error in the line :