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We report on properties of the viscous superlayer using direct simulation of a temporal plane jet at Re = 2500. The local entrainment velocity vn scales with the Kolmogorov velocity with a prefactor that depends on the enstrophy threshold. The entrainment flux vnS is practically independent of the threshold choice, as is observed from the mean entrainment velocity ue = vn S/A, where S is the enstrophy isosurface area and A is the surface area after projecting onto the homogeneous directions. A decomposition of vn into a mean and turbulent contribution indicates that turbulent fluctuations are the dominant mechanism by which the interface propagates even in this viscosity-dominated region of the flow.
Author(s):
Maarten van Reeuwijk
Imperial College
United Kingdom
Markus Holzner
ETH Zurich
Switzerland