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UDF for a Unsteady velocity change

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Old   April 28, 2006, 04:45
Default UDF for a Unsteady velocity change
  #1
Paul
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Hi,

I have a relatively simple problem involving writing a udf for a model but unsure how to set it up.

I am running a eulerian unsteady problem with a velocity of say 5 m/s. i want to run this for a set number of time steps and then increase the velocity to say 8 m/s, running this for a few seconds and then dropping it back down to the original 5 m/s. The aim is to see how the model copes with the increased mass flow.

Any help in the basic construction of a scheme would be much appreciated.

Paul
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Old   April 29, 2006, 00:35
Default Re: UDF for a Unsteady velocity change
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Mac
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Not to repeat the obvious, but if it's just for testing the response of the model, then why not run a usual case for say 5 m/s (lets say some X timesteps), then go to the boundary conditions panel and provide your step change to say 8 m/s and run it for some time and finally drop back to 5 m/s?
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Old   April 29, 2006, 00:36
Default Re: UDF for a Unsteady velocity change
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Joe
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Or alternately, you could use a journal file to achieve the same.
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Old   July 21, 2011, 14:25
Question Unsteady Temperature
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This seems like a little bit old thread but it addresses a very similar situation to what I am currently trying to achieve. I am a little new with fluent but I think this is quite easy to achieve: instead of having the velocity step switch it to a temperature change that ramps from ambient temp to lets say 400K, it stays like that for a couple of minutes and then it goes up again and stays like that for another while before it finally is left cool down to ambient temp again (about 300k). Can it be achieved with a similar approach or do I have to look into udfs?
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Old   July 22, 2011, 14:17
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You need not write UDF.

You can write a profile file. Read this profile file and hook this up in the inlet bc panel. Fluent user manual provides the information for writing this profile file
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Old   July 25, 2011, 15:33
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Nikhil,

thanks for your help. I had thought of using profiles before but unfortunately I am not very familiar and when I read the manual it didn't say much about creating your own profile. Anyways, I have tried creating one in notepad and then save it as .prof following the manual. Here is my "code" :

((transienttemp transient 4 0)
(time
0 10 40 50)
(temperature
300 1000 1000 600))

Following that I read the profile into fluent, went to the boundary conditions and specified the temperature of my desired wall as "transienttemp temperature" also to see if it worked I decided to create a surface monitor that would look at the static temperature of the surface every time step. However once the simulation is done I get no result except for the results of the final step t = 600, in the monitor plot there is nothing displayed. Do you know what I could be doing wrong? Thanks.
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Old   July 28, 2011, 13:45
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Maybe I have not been completely clear. I am not sure my approach is working since my surface monitor did not show anything. Is there a way to see the results at different time steps of a transient simulation?

Edit: I finally got it to work, if anyone is interested on knowing: You can create the profile code in notepad, ensure that your units are SI, that means t = secs. I was not seeing my results because I did the code thinking of minutes while the transient simulation ran in seconds thus comparing 50 secs to 3000 makes your plotted results very small. I am still unsure of how to see the results of different time steps of a transient simulation without having to create a case for each step.

Last edited by kike; July 29, 2011 at 13:18. Reason: Update
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Old   August 28, 2011, 01:48
Default velocity inlet for 3d parabolic equation.
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hiii friends i am entirely new to using udf's in fluent. I have a cubical geometry, with two inlets on perpendicular adjacent faces. i have to implement udf to only one of the conditions.
i have two cases
1) parabolic velocity inlet ( space varient)
2) sinusodial velocity velocity inlet ( time variant)
can any one pls send me the udf ( codes) ...
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Old   August 29, 2011, 02:19
Default udf help
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hiii friends i am entirely new to using udf's in fluent. I have a cubical geometry, with two inlets on perpendicular adjacent faces. i have to implement udf to only one of the conditions.
i have two cases
1) parabolic velocity inlet ( space varient)
2) sinusodial velocity velocity inlet ( time variant)
can any one pls send me the udf ( codes) ...
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