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Pressure spectra - FFT for pressure field

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Old   February 13, 2020, 10:40
Default Pressure spectra - FFT for pressure field
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Jiri
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Hello,


this is a question I asked in CFX forum but I would like to verify the capability of Fluent:

when doing a transient analysis in Fluent, can Fluent make FFT (or DFT) of pressure for each node on a surface in order that I could obtain pressure contour in the frequency domain?
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Old   February 13, 2020, 11:10
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Fluent does have FFT support but it can only be performed on a monitor. This means it is limited to points, a bunch of points, or surface integrals. You can get the pressure spectrum in frequency domain, but you can't do a multi-dimensional surface DFT and get spatial modes.


Also, doing this in Fluent, while convenient, also means the plot itself is stuck in Fluent. It's cumbersome to do follow-up post-processing. So keep that in mind.
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Old   February 13, 2020, 11:33
Default Spectrum vs point-value
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Whatever tool you use, you will have to decide which parameter and which value do you want to plot as contour. When FFT is done on, say pressure at a point, output is a profile and not a single value. To plot a contour, a value needs to be selected from the profile.
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Old   February 14, 2020, 03:57
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Thank you both for the recommendation. What are your suggestion then? I guess to export transient data points to an external FFT and then visualize the contour for selected frequency in Matlab? Or could you suggest any other tool for the visualization if you have any experience with this?
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Old   February 14, 2020, 06:22
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Yes, matlab or octave or tecplot or Fluent. Its a matter of convenience, I suppose. If you wish to plot contours on the domain itself, you can combine all the FFT profiles into a single one, bring those to Fluent, and then plot as contours on the the boundary. It's good to have a context. However, any other tool should show similar behavior if spatial coordinates are used to plot 3D contours.
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