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

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 May 29, 2013, 05:04 salam #41 New Member   tehran Join Date: May 2013 Posts: 3 Rep Power: 5 hi amir .can i ask u about sth about b.c with udf

 August 14, 2013, 12:05 Defining TOP HAT VELOCITY profile #42 New Member   Yunusrulz Join Date: Apr 2012 Posts: 10 Rep Power: 6 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: 5 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, 13:01 #44 Senior Member   Srivathsan N Join Date: Jan 2013 Location: India Posts: 101 Rep Power: 5 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: 5 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, 18:41 UDF for inlet y velocity 2D #46 New Member   Keyu Dhingani Join Date: Dec 2015 Location: San Diego, CA Posts: 3 Rep Power: 2 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, 04:58
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 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, 11:09 #48 Member   Rupesh Verma Join Date: Jun 2013 Posts: 64 Rep Power: 5 Dear u r right..

 October 24, 2016, 04:51 UDF for inlet temperature #49 New Member   mm Join Date: May 2016 Posts: 24 Rep Power: 2 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, 10:36 #50 Senior Member   Join Date: Nov 2013 Posts: 939 Rep Power: 12 Code: `else if (1300.0 < t && t <= 1500.0 )` should be Code: `else if ((1300.0 < t) && (t <= 1500.0 ))`

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