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-   -   Unsteady BC (http://www.cfd-online.com/Forums/fluent/27383-unsteady-bc.html)

Morvan Dominique November 25, 1999 09:38

Unsteady BC
 
I would wish to impose unsteady boundary conditions by using software FLUENT5 and them User Defined Function (UDF) in interpreted mode. I tested the example developed in documentation entitled: " Transient Velocity Inlet Profiles for Flow in A Tube " To impose a condition speed of the form: Vx=V0+Asin(wt) I used the following procedure:
#include "udf.h" DEFINE_PROFILE(unsteady_velocity,thread,position) { face_t_f; begin_f_loop(f,thread) { real t=RP_Get_Real("flow_time"); F_PROFILE(f,thread,position)=20.+5.*sin(10.t); } end_f_loop(f,thread)}
By looking at the time evolution of the speed at the exit of the tube, I do not find a sinusoidale curve ? Did somebody of other encounter the same problem? Thank you in advance

ali Oge November 25, 1999 12:04

Re: Unsteady BC
 
Hi Morvan,

I have done a lot calculation on pulsating flow in a muffler by using FLUENT 5. I have not faced any problem. I suggest you to monitor velocity variation especialy at the INLET and outlet boundaries at the each time step during the solution and check if your inlet velocity function is correct. And also, your time step should be enough small in order to define sine wave form of the inlet velocity.

Ali,


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