Thermal and vortical layers in transcritical wall turbulence

Fully-developed, turbulent boundary layers are characterized by zones of uniform momentum which are delineated by internal interfacial layers (IIL). The uniform momentum zones (UMZ) have been shown to be related to the underlying coherent structures in wall-bounded turbulence. A novel IIL identification method, proposed by Duosi et al., allows the characterization of an analogous thermal layer in the transcritical turbulent channel flow. The thermal internal interfacial layer (TIIL) delineate regions of homogeneous thermodynamic properties. The thermal and vortical interfaces are correlated but not collocated in the turbulent boundary layer. The TIILs are statistically located halfway between the wall and the IIL. Their existence and location can be understood through the prism of the attached eddy model which is highlighted by a strong correlation between the heights of both layers. Conditional sampling at the TIIL shows the presence of a strong thermal gradient which is not observed in the mean flow. The understanding of the thermal layering in transcritical flow permits a simplification of the wall scaling under complex thermodynamic conditions which will be discussed in this presentation.