FFT in FLUENT

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 March 23, 2008, 23:25 FFT in FLUENT #1 Thanathat Guest   Posts: n/a Dear All In the first sorry for my bad English. I have a problem about FFT in Fluent. I create a "point" in my fluid domain and need to collected the data for FFT ( Running by LES and use surface monitors , report type : mass flow rate , report of : Pressure , Static pressure )after I open the files all of my data show "0" all points. Can every body help me for this case.

 March 24, 2008, 01:37 Re: FFT in FLUENT #2 Sham Guest   Posts: n/a You need to change the scale I think. If you are after the peak freq., change the scale of x-axis from 0 to 1. Could you also tell me do you get a good results with LES? What approach do you take for LES modelling? Sham.

 March 24, 2008, 04:50 Re: FFT in FLUENT #3 Thanathat Guest   Posts: n/a Thank your for your help , do you mean the scale in surface monitor plot or where ???.

 March 24, 2008, 05:13 Re: FFT in FLUENT #4 Sham Guest   Posts: n/a scale in FFT graph

 March 24, 2008, 05:18 Re: FFT in FLUENT #5 Thanathat Guest   Posts: n/a I found this error Warning :Read_Signal: FFT can handle a costant sampling interval only! Jump in sampling interval at number 30 is more than 1 percen ! what does it mean ???

 March 27, 2008, 08:08 Re: FFT in FLUENT #6 Renato Pacheco Guest   Posts: n/a it means that your interval is very small. try increasing it, then u probably get your plot right.

 March 31, 2008, 09:38 Re: FFT in FLUENT #7 Thanathat Guest   Posts: n/a You mean Data sampling for time statistics ( sampling interval)or where ??

 March 31, 2008, 11:08 Re: FFT in FLUENT #8 Renato Pacheco Guest   Posts: n/a i mean when u go to axes, then u can select the interval of plotting. i had the same problem, and when i increased this interval of ploting(the range), it worked.

 August 14, 2009, 15:02 FFT warning #9 Senior Member   Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 114 Rep Power: 8 While taking FFT of a signal in Fluent I get the following warning Warning: Unknown x-function in Process_and_Plot_Signal function. Can anybody tell me what does it mean?

 August 15, 2009, 07:16 #10 New Member   abdul samad Join Date: Aug 2009 Posts: 14 Rep Power: 8 doesn't matter....ths s no error seucj likes this.

 August 15, 2009, 07:18 #11 New Member   abdul samad Join Date: Aug 2009 Posts: 14 Rep Power: 8 u r doing fft for sound amplitude or wt?

 August 15, 2009, 08:04 #12 Senior Member   Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 114 Rep Power: 8 no just simple FFT with ideal gas and transonic flow and density based solver. the problem is that I am getting very low value of Power Spectral Density on y axis (e-09) is it ok?

 August 15, 2009, 08:21 #13 New Member   abdul samad Join Date: Aug 2009 Posts: 14 Rep Power: 8 these values are pretty lesser........ perhaps if u can expalin ur case in detail...........i may help

 August 15, 2009, 09:21 #14 Senior Member   Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 114 Rep Power: 8 I am simulating unsteady flow over Ariane 5 rocket. The solver is density based explicit and time formulation is explicit as well. I think in this case the number of samples=no of iterations. I want to simulate till 1 m sec. When I get the FFT in between about 2e-04 second this situation arose which I just discussed. I am using URANS (with k omega model). for SA model I dont remember bt y axis but it gave me another warning that differnce in sample 1000 (I hope its 1000 iter because I increased CFL no there) is less than 1 %. Hope its clear now

November 2, 2009, 01:54
#15
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Morteza
Join Date: Nov 2009
Posts: 9
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Quote:
 Originally Posted by Sham ;149391 You need to change the scale I think. If you are after the peak freq., change the scale of x-axis from 0 to 1. Could you also tell me do you get a good results with LES? What approach do you take for LES modelling? Sham.
Hello my freind.
i guess u should use first K-epsilon model until ur residuals converges ,after that by inputting the:"solve/initialize/init-flow-statistics" in the text command.then u can choose the LES model.
good luck

 May 10, 2014, 07:32 #16 New Member   Charles Odijie Join Date: May 2014 Posts: 1 Rep Power: 0 I am new here, I registered few mins ago. I need help with reading FFT files. Non of the files that were saved during d calculation will loading into d fft. I'm trying to Plot d graphs on 'power spectral density, frequency and strouhal number. After d simulation, I clicked Plots/FFT/Set-up/Load Input files.... no file appeared. I scrolled down to All Files, and some file showed up, saved in .dat and .cas. When I tried to load one of d files, this error appeared: 'error reading file. What should I do?? I need help please.

 October 24, 2014, 10:46 #17 Member   kabilan.B Join Date: Jul 2010 Location: chennai Posts: 77 Rep Power: 7 how to define les model in fluent 6.3. thank you

 October 24, 2014, 14:07 #18 Senior Member   Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 114 Rep Power: 8 for les model you need to check on unsteady and the model should be 3D.

 October 25, 2014, 09:03 #19 Member   kabilan.B Join Date: Jul 2010 Location: chennai Posts: 77 Rep Power: 7 thank you sir..

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