  This article aims to make a detailed analysis of co-flowing plane Couette
flows. Particularly, the variation of flow quantities from the turbulent to
non-turbulent region is studied. While the enstrophy exhibits a sharp jump, the
other quantities (e.g., mean velocity, Reynolds normal stress, and kinetic
energy) show a continuous variation across the interface. The budget analysis
of Reynolds normal stresses reveals that the terms playing a key role in
turbulence transportation vary depending on the Reynolds normal stress under
study. The terms production, diffusion, and redistribution play an important
role in streamwise Reynolds stress {\dh}u0u0 {\TH}. In the spanwise Reynolds
stress {\dh}v0v0 {\TH}, the diffusion terms play a significant role. In the
wall-normal Reynolds stress {\dh}w0w0 {\TH}, only the redistribution term is
significant. The influence of one flow over another in the co-flow state was
observed through the additional mean velocity and Reynolds normal stress found
in the system compared to a standard plane Couette flow (pCf). Comparing the
co-flow system with a conventional pCf system, the former exhibits greater
vorticity, vortex stretching, and kinetic energy. A detailed analysis on the
geometry and topology of flow structures was studied using flow invariants.
