An experimental investigation of the turbulent cascade in a von Kármán mixing tank*

A series of volumetric velocimetry measurements have been performed in the highly turbulent center region of a von Kármán mixing tank. The measurements are taken at Re_λ=199, and consist of 200 000 independent samples of a cubic box of 42η^3, obtained using a Tomographic Scanning PIV technique. In addition, a Stereo PIV dataset was taken under the same conditions, consisting of 40 000 independent samples with a larger field of view (140η x 180η).

In the region of interest, we have investigated the inter-scale energy transfer using the Kármán-Howarth equation generalized for non-isotropic, inhomogeneous turbulence (sometimes referred to as the Kármán-Howarth-Monin-Hill equation). The data is spatially fully resolved, which allows us to directly compute the dissipation rate of the flow, together with all the terms of the energy balance. The results show a strong directional dependence of the kinetic energy distribution, in addition to anisotropy in a number of scale dependent energy transfer terms. This detailed characterization of the development of the turbulent field provides insight into the turbulent cascade in a flow configuration commonly employed to study the fine-scale structure of turbulence.