4.4 Article

Analysis of anisotropically permeable surfaces for turbulent drag reduction

Journal

PHYSICAL REVIEW FLUIDS
Volume 2, Issue 11, Pages -

Publisher

AMER PHYSICAL SOC
DOI: 10.1103/PhysRevFluids.2.114609

Keywords

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Funding

  1. Engineering and Physical Sciences Research Council [EP/M506485/1]
  2. Engineering and Physical Sciences Research Council [1497964] Funding Source: researchfish

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The present work proposes the use of anisotropically permeable substrates as a means to reduce turbulent skin friction. We conduct an a priori analysis to assess the potential of these surfaces, based on the effect of small-scale surface manipulations on near-wall turbulence. The analysis, valid for small permeability, predicts a monotonic decrease in friction as the streamwise permeability increases. Empirical results suggest that the drag-reducing mechanism is however bound to fail beyond a certain permeability. We investigate the development of Kelvin-Helmholtz-like rollers at the surface as a potential mechanism for this failure. These rollers, which are a typical feature of turbulent flows over permeable walls, are known to increase drag and their appearance is known to limit the drag-reducing effect. We propose a model, based on linear stability analysis, that predicts the onset of these rollers for sufficiently large permeability and allows us to bound the maximum drag reduction that these surfaces can achieve.

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