turbulence*

The shape of the turbulent energy spectrum at high Taylor-scale Reynolds numbers (R_λ) has been investigated in numerical, laboratory, and field experiments. It is important for both the fundamental understanding of turbulence and for tests of LES and its numerous applications. 

The Variable Density Turbulence Tunnel (see Bodenschatz et al. (2014)) exploits the capabilities of a unique active grid to produce turbulent flows up to R_λ ~6000. We use NSTAPs provided by Princeton University (e.g. Kunkel et al. (2006), Bailey et. al. (2010), Fan et al. (2015)) to acquire two-point statistics of high resolution. By combining the flexibility of the active grid and different densities we will present a relative energy spectrum almost free of probe biases. This purely experimental approach is accompanied by numerical simulations to quantify and eliminate such biases resulting in absolute energy spectra. 

We find that two features of the energy spectrum show variations with R_λ. We can quantify for the first time (to the best of our knowledge) in a classical wind tunnel experiment how the bottleneck effect gets weaker with increasing R_λ. We further identify a R_λ-dependence of the intermittency corrections to K41-predictions of the spectral slope.