super scale structure

By using Fourier transform, the original streamwise velocity component u can be decomposed into a large part (with streamwise wave length larger than 4h, and spanwise wave length larger than h), and a small part.

The super scale structure from the large part is shown by red (u'=0.1), and the small scale structure from the small part is shown by green (u'=0.1). Then the interaction between those two can be studied further.