Scaling of the turbulent/non-turbulent interface in boundary layers

Abstract

Scaling of the interface that demarcates a turbulent boundary layer from the non-turbulent free stream is sought using theoretical reasoning and experimental evidence in a zero-pressure-gradient boundary layer. The data-analysis, utilising particle image velocimetry (PIV) measurements at four different Reynolds numbers (Δuτ/ν = 1200-14 500), indicates the presence of a viscosity dominated interface at all Reynolds numbers. It is found that the mean normal velocity across the interface and the tangential velocity jump scale with the skin-friction velocity uτ and are approximately uτ/10 and uτ, respectively. The width of the superlayer is characterised by the local vorticity thickness δω and s..