FFT in FLUENT
 

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.

Re: FFT in FLUENT
 

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.

Re: FFT in FLUENT
 

Thank your for your help , do you mean the scale in surface monitor plot or where ???.

Re: FFT in FLUENT
 

scale in FFT graph

Re: FFT in FLUENT
 

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 ???

Re: FFT in FLUENT
 

it means that your interval is very small. try increasing it, then u probably get your plot right.

Re: FFT in FLUENT
 

You mean Data sampling for time statistics ( sampling interval)or where ??

Re: FFT in FLUENT
 

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.

FFT warning
 

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?

doesn't matter....ths s no error

u r doing fft for sound amplitude or wt?

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?

these values are pretty lesser........
perhaps if u can expalin ur case in detail...........i may help

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 :)

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:)

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.

how to define les model in fluent 6.3.
thank you

for les model you need to check on unsteady and the model should be 3D.

thank you sir..

non dimensional time step
 

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?