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Transient Velocity Inlet (2d synthetic jet) UDF 

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July 30, 2016, 10:32 
Transient Velocity Inlet (2d synthetic jet) UDF

#1 
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Join Date: Oct 2015
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Hello all
my case is consisted of a flow over a hump with a synthetic jet in the interior of the hump. essentially the jet is required to blow and suck air with a frequency of 138.5 Hz at an approximate velocity out of the slot of the jet of 26.6 m/s prescribed as : u=o v= speed*cos(2*pi*f) I'm fairly new in setting up User defined functions for boundary conditions, from digging around this forum and the literature the UDF for this particular case seems to be simple enough to formulate, but im getting some divergence after certain number of iterations. i wanted to double check whether im implementing the UDF correctly for the desired purpose. im using a pressure outlet boundary condition to hook the UDF /************************************************** ********************/ /* unsteady.c */ /* UDF for specifying a transient velocity profile boundary condition */ /************************************************** ********************/ #include "udf.h" DEFINE_PROFILE(SJ_velocity, thread, position) { face_t f; begin_f_loop(f, thread) { real freq=138.5; real t = RP_Get_Real("flowtime"); F_PROFILE(f, thread, position) = 26.6*cos(freq*(t)*(2.*3.141592654)); } end_f_loop(f, thread) I was wondering if someone could point me in the right direction on implementing this function for this particular case much appreciated David 

July 31, 2016, 09:38 

#2 
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please guys any help will be greatly appreciated


August 13, 2016, 12:12 

#3 
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Mike
Join Date: Jul 2016
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OK. I guess here's the problem. From 0 to pi/2 the velocity is positive so there is no problem and the problem is being solved. but after this point you got negative velocity at the inlet so that's where the divergence occurs because the flow is getting out the domain and the outlet boundary condition cannot stand this condition. OK try this: set an average velocity at a value that is larger than the amplitude of the oscillation. So the velocity of the inlet port will never get negative. Then see how's the results.


July 30, 2018, 04:04 
3D synthetic jet

#4 
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Arun jacob
Join Date: Jul 2018
Posts: 3
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I am working on synthetic jet flow simulation. i want to know that how can i generate a 3d UDF for the following parameters velocity = 195m/sec, Frequency is 17.
I am also attaching the udf generated in 2d. Now i want to do the same in 3D..what are the changes that i should made to get the result. #include"udf.h" DEFINE_PROFILE(SJ_velocity,thread,position) { face_t f; begin_f_loop(f,thread) { real freq=17; real t= RP_Get_Real("flowtime"); F_PROFILE(f,thread,position) =195*sin(freq*(t)*(2.*3.141592654)); } end_f_loop(f,thread) } Last edited by Arun Jacob; July 30, 2018 at 04:13. Reason: some part missing 

October 18, 2018, 02:31 
3d synthetic jet

#5 
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Vilas
Join Date: Oct 2018
Location: Pune maharashtra,india
Posts: 13
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Sir.
I have also same problem can you help me. 

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transient 2d, udf, user defined b.c. 
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