# (ask) how to create UDF for inlet velocity profile

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 May 29, 2013, 06:04 salam #41 New Member   tehran Join Date: May 2013 Posts: 4 Rep Power: 10 hi amir .can i ask u about sth about b.c with udf

 August 14, 2013, 13:05 Defining TOP HAT VELOCITY profile #42 New Member   Yunusrulz Join Date: Apr 2012 Posts: 10 Rep Power: 11 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.

 January 14, 2014, 05:58 Velocity inlet UDF in fluent #43 New Member   Akshay Khadse Join Date: Sep 2013 Posts: 11 Rep Power: 10 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?

 July 9, 2014, 14:01 #44 Senior Member   Srivathsan N Join Date: Jan 2013 Location: India Posts: 101 Rep Power: 10 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? Thanks in advance __________________ Regards, Srivaths

 January 12, 2016, 11:03 Periodic BC DDPM, UDF #45 Member   Rupesh Verma Join Date: Jun 2013 Posts: 64 Rep Power: 10 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. Thanks for helping in advance!!!

 April 25, 2016, 19:41 UDF for inlet y velocity 2D #46 New Member   Keyu Dhingani Join Date: Dec 2015 Location: San Diego, CA Posts: 3 Rep Power: 7 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

April 26, 2016, 05:58
#47
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Quote:
 Originally Posted by Keyu 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.

 April 27, 2016, 12:09 #48 Member   Rupesh Verma Join Date: Jun 2013 Posts: 64 Rep Power: 10 Dear u r right..

 October 24, 2016, 05:51 UDF for inlet temperature #49 New Member   mm Join Date: May 2016 Posts: 24 Rep Power: 6 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" DEFINE_PROFILE(inlet_temperature,thread,position ) { face_t f; begin_f_loop(f,thread) { real t = RP_Get_Real("flow-time"); if (t <=1300.0 ) { F_PROFILE(f,thread,position) = 379.13 + 0.0005*t; } 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); } } end_f_loop(f,thread) }

 October 24, 2016, 11:36 #50 Senior Member   Join Date: Nov 2013 Posts: 1,947 Rep Power: 24 Code: `else if (1300.0 < t && t <= 1500.0 )` should be Code: `else if ((1300.0 < t) && (t <= 1500.0 ))`

 January 25, 2017, 03:16 Sinus velocity #51 New Member   milad Join Date: Jan 2017 Posts: 4 Rep Power: 6 Hello I have a question How write( V=Asinwt) in fluent(udf) Please help me Thank you

 January 25, 2017, 03:47 #52 Senior Member   Join Date: Nov 2013 Posts: 1,947 Rep Power: 24 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. KevinZ09 likes this.

 January 25, 2017, 23:39 Sinus velocity #53 New Member   milad Join Date: Jan 2017 Posts: 4 Rep Power: 6 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

 January 26, 2017, 03:56 #54 Senior Member   Join Date: Nov 2013 Posts: 1,947 Rep Power: 24 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!

 January 28, 2017, 13:11 how to use data from .csv file as inlet boundry condition #55 New Member   hemant mittal Join Date: Feb 2016 Posts: 21 Rep Power: 7 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 SimonaM likes this.

January 30, 2017, 05:08
#56
New Member

SAIF MASOOD
Join Date: Sep 2016
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Quote:
 Originally Posted by Amir 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.
fluentp1-1-02000.jpg

t.jpg

 February 11, 2017, 10:54 Error message : output pipe has been closed #57 New Member   Thomas henderson Join Date: Feb 2017 Posts: 3 Rep Power: 6 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?

 February 13, 2017, 05:29 #58 Senior Member   Join Date: Nov 2013 Posts: 1,947 Rep Power: 24 Which one is "this UDF"?

February 13, 2017, 05:50
Udf
#59
New Member

Thomas henderson
Join Date: Feb 2017
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Quote:
 Originally Posted by pakk Which one is "this UDF"?
#include "udf.h"

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

vel= 0.2+0.1*sin(t);

{

}

 February 14, 2017, 12:45 Syntax error #60 New Member   Thomas henderson Join Date: Feb 2017 Posts: 3 Rep Power: 6 There is a syntax error in the line : DEFINE_PROFILE(unsteady_velocity, thread, position) However this is similar to other examples I have seen. Any ideas why this may be?

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