  Counter-flow or counter-current configurations can maintain high turbulence
intensities and exhibit a significant level of mixing. We have previously
introduced a wall-bounded counter-flow turbulent channel configuration
(Physical Review Fluids, 6(9), p.094603.) as an efficient framework to study
compressibility effects on turbulence. Here, we extend our previous direct
numerical simulation study to a relatively higher Mach number (M=0.7) to
investigate strong compressibility effects (also by reducing the Prandtl number
from Pr=0.7 to 0.2), and the formation and evolution of unsteady shocklet
structures. It is found that the configuration is able to produce highly
turbulent flows with embedded shocklets and significant asymmetry in
probability density functions of dilatation. A peak turbulent Mach number close
to unity is obtained, for which the contribution of the dilatational
dissipation to total dissipation is nevertheless found to be limited to 6%.
