Dynamics of spatial Fourier modes in turbulence

We present the results of an experimental study of the spatial Fourier modes of the vorticity in a turbulent jet flow. By means of an acoustic scattering setup we have recorded the evolution in time of Fourier modes of the vorticity field, characterized by well defined wavevectors <Emphasis Type="Bold">k. By computing the auto-correlation of the amplitude of the Fourier modes we evidence that, whatever the length scale (or equivalently <Emphasis Type="Bold">k), the dynamic evolution of the vorticity field involves two well separated time scales. We have also performed the simultaneous acquisitions of pairs of Fourier modes with two wavevectors <Emphasis Type="Bold">k and <Emphasis Type="Bold">k'. Whatever the spectral gap <Emphasis Type="Bold">k- <Emphasis Type="Bold">k', any pair of Fourier modes exhibits a significant cross-correlation over long time delays, indicating a strong statistical dependence between scales. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006