Hi!
I am trying to generate turbulence in a wind tunnel (1148mm X 814mm). I need longerlength scales(longitudenal) at lower turbulence intensities. I have used typical grids with the ratio of spacing to teh bar thickness being 4 and 5. I have tried bars as wide as 400mm. the max. length scales I could achieve was 0.11m . According to Vickery the max. length scales cannot be longer than 13% of the width of the tunnel, that would mean a max. of 0.15m length scales, however I havent been able to achieve this.
The turbulence has to be uniform across the cross section.
I am using Hotwire annemometry for analysing the flow properties. the length scales are found by matching the spectra with the von'karman spectra (length scale being the variable parameter).

Thanks in advance