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Plot Turbulence Spectrum Using 2D Spatial FFT 

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October 21, 2021, 08:31 
Plot Turbulence Spectrum Using 2D Spatial FFT

#1  
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Jeffrey Johnston
Join Date: Oct 2020
Location: Belfast, Northern Ireland
Posts: 21
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Hello!
I am trying to replicate the results of a study (here) that performs LES of an atmospheric boundary layer. One of the results produced is a turbulence spectrum. I want to recreate this, but I'm a bit lost. Here's the description in the paper: Quote:
My second point of confusion is how to obtain a single 2axis plot from a 2D fft. Performing a fft of the 2D array of velocity magnitudes produces a 2D array of velocity intensities. I assume that this resultant array is what the we call "wavespace"? But what is a wavevector? How do I find ones of equal magnitude and sum them? And what are the concentric rings all about? Many thanks, 

October 21, 2021, 13:23 

#2  
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Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,290
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Quote:
Often one performs the FFT of a velocity component, the corresponding Fourier coefficient is "squared" and you have dimensionally one component of the kinetic energy. There are theoretical reasons to deduce that. In the paper the 2D plot is reduced to a 1D plot along the unique k wavenumber computed as described, for different rings. 

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fft, les, spectral analysis, turbulence, waves 
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