# How to calculate wavenumber while using fft?

 Register Blogs Members List Search Today's Posts Mark Forums Read June 23, 2019, 08:09 How to calculate wavenumber while using fft? #1 Senior Member   Join Date: Jan 2018 Posts: 121 Rep Power: 7 I have 192 grids of two point correlation data of a 3.14(m) length domain. I use the "fft" command in matlab to plot the energy spectrum. How can I calculate wavenumber(k) of each grid? Code: ```R= load('2pcor.txt'); PHI = fft(R); % K=?? ; %loglog(K,abs(PHI));```   June 23, 2019, 12:12 #2
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Filippo Maria Denaro
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 Originally Posted by KevinSpears I have 192 grids of two point correlation data of a 3.14(m) length domain. I use the "fft" command in matlab to plot the energy spectrum. How can I calculate wavenumber(k) of each grid? Code: ```R= load('2pcor.txt'); PHI = fft(R); % K=?? ; %loglog(K,abs(PHI));```

On your grid of Nx=192 nodes you have 192/2=96 resolvable wavenumbers. Each wavelength is k=n*2*pi/L. Thus, if you L is exactly pi (in meters) you have k=2*n. The maximum in your range is the Nyquist frequency pi/h=pi/(L/Nx)=Nx

Last edited by FMDenaro; June 23, 2019 at 16:16.  Tags fft, matlab, turbulence Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post Roh FLUENT 5 February 21, 2022 11:30 Roh FLUENT 1 June 17, 2018 03:12 soheil1991 FLUENT 3 March 11, 2017 09:30 manish CFX 4 March 15, 2007 02:57 K S Chang Main CFD Forum 6 January 15, 2004 06:42

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