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FFT in FLUENT

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Old   March 23, 2008, 23:25
Default FFT in FLUENT
  #1
Thanathat
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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.
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Old   March 24, 2008, 01:37
Default Re: FFT in FLUENT
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Sham
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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.
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Old   March 24, 2008, 04:50
Default Re: FFT in FLUENT
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Thank your for your help , do you mean the scale in surface monitor plot or where ???.
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Old   March 24, 2008, 05:13
Default Re: FFT in FLUENT
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Sham
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scale in FFT graph
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Old   March 24, 2008, 05:18
Default Re: FFT in FLUENT
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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 ???
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Old   March 27, 2008, 08:08
Default Re: FFT in FLUENT
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Renato Pacheco
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it means that your interval is very small. try increasing it, then u probably get your plot right.
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Old   March 31, 2008, 10:38
Default Re: FFT in FLUENT
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You mean Data sampling for time statistics ( sampling interval)or where ??
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Old   March 31, 2008, 12:08
Default Re: FFT in FLUENT
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Renato Pacheco
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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.
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Old   August 14, 2009, 16:02
Default FFT warning
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Shamoon Jamshed
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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?
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Old   August 15, 2009, 08:16
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abdul samad
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doesn't matter....ths s no error
seucj likes this.
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Old   August 15, 2009, 08:18
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u r doing fft for sound amplitude or wt?
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Old   August 15, 2009, 09:04
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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?
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Old   August 15, 2009, 09:21
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these values are pretty lesser........
perhaps if u can expalin ur case in detail...........i may help
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Old   August 15, 2009, 10:21
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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
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Old   November 2, 2009, 01:54
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Morteza
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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
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Old   May 10, 2014, 08:32
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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.
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Old   October 24, 2014, 11:46
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how to define les model in fluent 6.3.
thank you
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Old   October 24, 2014, 15:07
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for les model you need to check on unsteady and the model should be 3D.
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Old   October 25, 2014, 10:03
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thank you sir..
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Old   March 26, 2018, 14:00
Default non dimensional time step
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hi i have problem to find non dimensional time step
this formul is ut/D and D=0.04 , U According to Re=100 dansity=1000 and viscosity=0.001002
it will be obtained U=0.0025m/s non dimensional time will bw obtained 77 how can do it?
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