Oscillating grid generating turbulence near gas-liquid interfaces in shear-thinning dilute polymer solutions

Understanding the behavior of liquid phase turbulence near gas-liquid interfaces is of great interest in many fundamental, environmental, or industrial applications. For example, near-surface liquid side turbulence is known to enhance the mass transfers between the two phases. Descriptions of this behavior for air-water systems exist in the literature, but the case of turbulence in a shear-thinning liquid phase below a flat gas-liquid interface has never been considered to the best of our knowledge. This paper consists in an experimental characterization of low Reynolds number, oscillating grid generated, near-surface turbulence in shear-thinning dilute polymer solutions, in the surface-influenced and in the viscous sublayers. The energy transfer mechanism, known in the water case, is evidenced in dilute polymer solutions. A horizontal damping mechanism, similar to the one introduced by surfactants, is evidenced. The evolution of the viscous sublayer depth can be explained by both viscous and shear-thinning effects, and it appears that a critical polymer concentration may exist within the dilute regime.