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

Jovan Nedic
Department of Mechanical Engineering McGill University, Canada

Stavros Tavoularis
Department of Mechanical Engineering, University of Ottawa, Ottawa, Ontario KIN 6N5, Canada

Sinopsis

The fine and large−scale properties in spatially developing uniformly sheared flow (USF) and USF distorted by a square−mesh grid was examined experimentally using one− and two−point, two−component hot−wire anemometry. We confirmed previous findings that USF has an intermediate region where the dissipation parameter scales with the local turbulent Reynolds number as Cε ∝ Reλ−0.6 and a far downstream region, where Cε ~ const.. The insertion of a grid across the USF resulted in the creation of multi-structure turbulence and a permanent reduction of kinetic energy and length scales of the turbulence. Near the grid the dissipation parameter scaled as Cε ∝ Reλ−1, as in decaying grid turbulence, despite the opposite evolution rates of the kinetic energy (and 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 by the grid. Second−order structure functions, normalised by Kolmogorov scales, collapsed in the viscous sub−range, as well as for the largest measured separations. Within the inertial sub−range, however, the effects of grid insertion were measurable.