# impose same velocity at inlet

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July 29, 2013, 12:36
impose same velocity at inlet
#1
Member

rayan
Join Date: Jun 2013
Posts: 65
Rep Power: 6
I want to impose by UDF a same velocity profile in 3 inlets, but i don't get same velocity in the 3 inlets apparently i impose my profile in function of the distance r!!

how can i impose my velocity profile in the "surface" of inlet to get samevelocity please??

my udf is :
include "udf.h"
Quote:
 DEFINE_PROFILE(z_velocity_inlet,t,i) { real x[ND_ND]=3; real r; face_t f; begin_f_loop(f,t) { F_CENTROID(x,f,t); r = x[0]; F_PROFILE(f,t,i) = -((0.0431*pow(r,3))-(0.3857*pow(r,2))+(0.3129*r)+8.8045); } end_f_loop(f,t)
Thanks

 July 29, 2013, 14:14 #2 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,651 Rep Power: 26 Apparently, you are using the absolute value of the x-coordinate for each of the 3 inlets. If they dont have identical position, the velocity will be different. I already tried to point this out in your last thread concerning this topic Additionally, "real x[ND_ND]=3;" is some kind of strange. You initialize the value 3 to the variable x here, which makes no sense as it is overwritten anyway. Use "real x[ND_ND];" instead. rayan24 likes this.

 July 30, 2013, 03:02 #3 Member   rayan Join Date: Jun 2013 Posts: 65 Rep Power: 6 Thanks Alex for your replay, I confirme that the inlets are diffrents coordinate of X, so how can i specify this difference in UDF please

 July 30, 2013, 03:12 #4 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,651 Rep Power: 26 Write 3 similar UDFs and shift the coordinate to match the "local" coordinate system of each inlet. Change the variable "offset" so that r actually becomes the distance (I suppose distance from the wall?) in each inlet. Code: `r = x[0]-offset;` If you are having trouble with this, we will need a sketch of your setup and the velocity profiles you want in order to give further advice. rayan24 likes this.

 July 30, 2013, 03:26 #5 Member   rayan Join Date: Jun 2013 Posts: 65 Rep Power: 6 Thank you very much Alex that's what I did , I needed your confirmation! its OK but in the results of simulation I feel that the velocity is not properly difffuse ? (i use RSM model) do you have an idea ?

 July 30, 2013, 04:07 #6 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,651 Rep Power: 26 I dont know what you mean by "the velocity is not properly diffuse".

 July 30, 2013, 04:53 #7 Member   rayan Join Date: Jun 2013 Posts: 65 Rep Power: 6 It's okay, it was just a display problem Thank you Alex for your answers and help

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