Spectral Analysis of the Spatially Evolving Turbulent Channel Flow

The elementary structures of wall turbulence that carry most of the kinetic energy and momentum are typically referred to as energy-containing eddies (energy-eddies). Despite the general agreement that energy-eddies can sustain themselves at all relevant length scales [1, 2], their exact genesis and spatial evolution are still not well understood. In this study, energy-eddies at the inflow of a turbulent minimal-channel flow direct numerical simulation (DNS) are quenched and the spatial development of these eddies is studied at a friction Reynolds number \(Re_{\tau } = 550\) . Two synchronised DNSs are used in the current study: one is a fully resolved streamwise periodic channel flow, which is subsequently denoted as PCH-DNS, while the other is a fully resolved channel flow DNS with inflow-outflow boundary conditions, which will be denoted as IOCH-DNS. In the IOCH-DNS the inlet boundary condition is an inflow velocity field, which is a filtered version of the inflow of the PCH-DNS, with a convective outflow boundary condition applied at the domain exit [3]. The results demonstrate that energy-eddies are essential to maintain the eddies involved in the energy cascade. The results also show that the turbulent transport is the dominant transport term in the recovery of energy-eddies, and the energy-cascade eddies are primarily regenerated through wall-normal or scale-to-scale TKE transfer, rather than local production.