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-   -   UDF for a Unsteady velocity change (http://www.cfd-online.com/Forums/fluent/40773-udf-unsteady-velocity-change.html)

Paul April 28, 2006 04:45

UDF for a Unsteady velocity change
 
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

Mac April 29, 2006 00:35

Re: UDF for a Unsteady velocity change
 
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?

Joe April 29, 2006 00:36

Re: UDF for a Unsteady velocity change
 
Or alternately, you could use a journal file to achieve the same.

kike July 21, 2011 14:25

Unsteady Temperature
 
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?

nikhil July 22, 2011 14:17

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

kike July 25, 2011 15:33

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.

kike July 28, 2011 13:45

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.

niravtm007 August 28, 2011 01:48

velocity inlet for 3d parabolic equation.
 
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) ...

niravtm007 August 29, 2011 02:19

udf help
 
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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