title: Mechanics of the turbulent-nonturbulent interface of a jet.
abstract: We report the results of an experimental investigation of the mechanics and transport processes at the bounding interface between the turbulent and nonturbulent regions of flow in a turbulent jet, which shows the existence of a finite jump in the tangential velocity at the interface. This is associated with small-scale eddying motion at the outward propagating interface (nibbling) by which irrotational fluid becomes turbulent, and this implies that large-scale engulfment is not the dominant entrainment process. Interpretation of the jump as a singular structure yields an essential and significant contribution to the mean shear in the jet mixing region. Finally, our observations provide a justification for Prandtl's original hypothesis of a constant eddy viscosity in the nonturbulent outer jet region.
authors.affiliation: Laboratory for Aero and Hydrodynamics, Delft University of Technology, 2628 CA Delft, The Netherlands. J.Westerweel@wbmt.tudelft.nl
authors.forename: J
authors.initials: J
authors.lastname: Westerweel
authors.forename: C
authors.initials: C
authors.lastname: Fukushima
authors.forename: J M
authors.initials: JM
authors.lastname: Pedersen
authors.forename: J C R
authors.initials: JC
authors.lastname: Hunt