Mass transport induced by a jet impinging on a density interface: The role of interfacial wave breaking

We report the experimental measurements of mass transport induced by a jet impinging a density interface. Using water/salt-water laboratory experiments, we investigate the mechanism of mass entrainment by performing simultaneous velocity and density measurements. We observe that the mass transport leading to the homogenisation of the density is due to the contribution of the mean fields, whereas the turbulent mass flux acts against the entrainment mechanism. Moreover, the turbulent mass flux is almost perpendicular to the density gradient in the impinged region, in contradiction with the classical eddy turbulent diffusion model. We interpret all these features in the framework of interfacial waves breaking. We show how the waves generate a mean flow leading to an enhancement of the entrainment process, and how the turbulent mass flux is correlated to the wave breaking. Finally, we discuss the relevance of the closure schemes used in numerical models (e.g., Reynolds Averaged Navier-Stokes (RANS) equations) to simulate this process. Copyright (C) EPLA, 2017