Abstract: We show that the physics of a turbulent/turbulent interface (TTI) are different from those of a turbulent/non-turbulent interface (TNTI), with inertial vorticity stretching being wholly responsible for creating the enstrophy discontinuity in the former, whilst viscous diffusion dominates in the outermost region of the latter. We show how the entrainment velocity evolves spatially across a TTI formed between a planar-wake and turbulent backgrounds of various characteristic turbulence intensities and length scales. Background turbulence is shown to enhance entrainment in the near-wake where both nibbling and engulfment are active, whilst it suppresses entrainment in the far-wake where nibbling is the predominant entrainment mechanism. Finally, we consider the entrainment of streamwise momentum and kinetic energy and show that the presence of background turbulence can modify the efficiency with which these quantities are entrained with respect to mass but these effects are only important in the near-wake.

Curriculum Vitae: Oliver Buxton is a professor of fluid mechanics at Imperial College in London in the UK. He is a fellow of the Royal Aeronautical Society, an advisory committee member to the UK Turbulence Consortium, and a former winner of the Europe-wide da Vinci award for young researchers in the fields of flow, turbulence, and combustion. His research interests include wind-turbine wakes, currently supported through an EPSRC fellowship, and cloud microphysics supported through an ERC consolidator grant, both of which are built on his work on fundamentals of turbulence including TNTIs and turbulent/turbulent interfaces.