  The impact of intrinsic compressibility effects -- changes in fluid volume
due to pressure variations -- on high-speed wall-bounded turbulence has often
been overlooked or incorrectly attributed to mean property variations. To
unambiguously quantify these intrinsic compressibility effects, we perform
direct numerical simulations of compressible turbulent channel flows with
nearly uniform mean properties. Our simulations reveal that intrinsic
compressibility effects yield a significant upward shift in the logarithmic
mean velocity profile that can be attributed to the reduction in the turbulent
shear stress. This reduction stems from the weakening of the near-wall
quasi-streamwise vortices. We in turn attribute this weakening to the
spontaneous opposition of sweeps and ejections from the near-wall expansions
and contractions of the fluid, and provide a theoretical explanation for this
mechanism. Our results also demonstrate that intrinsic compressibility effects
are responsible for the increase in the inner-scaled streamwise turbulence
intensity in compressible flows compared to incompressible flows, previously
regarded to be an effect of mean property variations.
