A case study of multi-structure turbulence: Uniformly sheared flow distorted by a grid

The fine and large-scale structures of spatially developing uniformly sheared flow (USF) and USF distorted by a square-mesh grid were examined experimentally using one- and two-point, two-component hot-wire anemometry. In agreement with previous findings, it was confirmed that USF has a far downstream region, where the dissipation parameter Cε is approximately constant, and an intermediate region, where it scales with the local turbulent Reynolds number as Cɛ∝Reλ−0.6. The insertion of a grid across the USF resulted in the creation of multi-structure turbulence (a flow in which at least two kinds of dominant eddies exist and contribute significantly to the local averages at the energy-containing level) and a permanent reduction of the kinetic energy and the integral length scales of the turbulence. Near the grid the dissipation parameter scaled as Cɛ∝Reλ−1, as in decaying grid turbulence, despite the opposite evolution rates of Reλ in the two flows. The turbulence fine structure within this multi-structure region was unaffected significantly by the grid, whereas the large-scale anisotropy was markedly changed. Second-order structure functions, normalised by Kolmogorov scales, collapsed in the viscous sub-range , whereas within the inertial sub-range the effects of grid insertion were measurable.