Abstract
Low Reynolds number turbulent flow in a lubricated plane channel is studied by means of direct numerical simulations. The very thin lubricating film is more viscous than the bulk-fluid and is present at both channel walls. The bulk-fluid is no longer exposed to the no-slip condition at the solid surfaces. Despite the rather large interfacial motions the bulk-flow does in many aspects perceive the interface as a solid wall, except in the immediate vicinity of the lubricating film where the interfacial motions heavily influence the bulk-flow. The lubricating film shows a high degree of anisotropy, and the only major component is the streamwise velocity fluctuations. Also the bulk-flow adjacent to the interface is closer to one-component turbulence than what is commonly observed close to solid surfaces. The interface is populated by very organized low-speed streaks with a mean spacing close to 100 wall units. The coherent structures in the near-interface region do resemble those close to solid walls, but they are situated somewhat closer to the interface since the coherent velocity field is slightly penetrating the lubricating film.
Published Version
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