The coherent structure of the kinetic energy transfer in shear turbulence

Abstract

The cascade of energy in turbulent flows, i.e., the transfer of kinetic\nenergy from large to small flow scales or vice versa (backward cascade), is the\ncornerstone of most theories and models of turbulence since the 1940s. Yet,\nunderstanding the spatial organisation of kinetic energy transfer remains an\noutstanding challenge in fluid mechanics. Here, we unveil the three-dimensional\nstructure of the energy cascade across the shear-dominated scales using\nnumerical data of homogeneous shear turbulence. We show that the characteristic\nflow structure associated with the energy transfer is a vortex shaped as an\ninverted hairpin followed by an upright hairpin. The asymmetry between the\nforward and backward cascade arises from the opposite flow circulation within\nthe hairpins, which triggers reversed patterns in the flow.\n