2D to 3D turbulence
 

Hi!
I want to perform a cheap DNS for a rectangular jet surrounded by coflow.
The geometric configuration is-
inhomogeneous normal in y-dir
inhomogeneous streamwise in z-dir
homogeneous spanwise x-dir is periodic


The question is what should be the domain extent in x direction
so that I get a 3D turbulence and not a 2D one.
Can you suggest (or refer) domain extent in terms of geometry(slot width) or integral scale?

Thanks apriori