Turbulent-nonturbulent interfaces in spatially developing compressible turbulent boundary layers.

An investigation of the characteristics of the turbulent-nonturbulent interface (TNTI) in spatially developing compressible turbulent boundary layers is performed by using a direct numerical simulation. The mean thicknesses of the TNTI layer δ_{TNTI} is approximately 13η_{ref} (η_{ref} is the Kolmogorov scale taken from a location of 0.3δ_{ref} from the outer edge of the TNTI layer, where δ_{ref} is the nominal thickness of the boundary layer) and the two components of the TNTI layer, viscous superlayer δ_{VSL} and turbulent sublayer δ_{TSL}, are approximately 3.6η_{ref} and 9.4η_{ref}, respectively. The multiscale analyses of the TNTI shows that the interscale energy transfer T_{r_{1}} in the direction normal to the TNTI layer are from large to small scales, while T_{r_{1}} is expressed as energy input in the entire range of scales in the direction close to the interface's tangent plane. However, this is the opposite for that in T_{r_{2}}, as the interscale energy transfer T_{r_{2}} in the direction normal to the TNTI layer are almost from small to large scales, while T_{r_{2}} is expressed as energy output in the entire range of scales in the direction close to the interface's tangent plane. The numerical results reported are expected to shed light on the accurate modeling and predicting of the spatially developing turbulent flows.