  We have performed direct numerical simulations (DNS) of compressible
turbulent channel flow at supercritical pressure with top and bottom isothermal
walls kept respectively at a supercritical (Ttop > Tpb) and subcritical
temperature (Tbot < Tpb), where Tpb is the pseudoboiling temperature. The DNS
are conducted using a high-order discretization of the fully compressible
Navier-Stokes equations in conservative form closed with the Peng-Robinsion
(PR) state equation. Bulk density is adjusted to obtain a bulk pressure of
approximately pb = 1.1pcr where pcr is the critical pressure of the working
fluid. Top-to-bottom temperature differences investigated are DT = 5 K, 10 K,
and 20 K, where Ttop/bot = Tpb +- DT / 2; buoyancy effects are neglected.
Varying DT modifies the average location of pseudophase change from ypb/h =
-0.23 (DT = 5 K) to 0.89 (DT = 20 K), where h is the channel half-height and y
= 0 the centerline position. Real-fluid effects cause visible deviations from
classical scaling laws in the mean velocity profile. Enstrophy generation due
stretching and tilting decreases with DT. The proximity to the
pseudotransitioning layer inhibits the intensity of the velocity fluctuations,
while enhancing the density and temperature fluctuations. Conditional
probability analysis reveals that the sheet of fluid undergoing pseudophase
change is characterized by a dramatic reduction in the kurtosis of density
fluctuations and becomes thinner as DT is increased. Instantaneous
visualizations show dense fluid ejections from the pseudoliquid viscous
sublayer, some reaching the channel core, causing positive values of density
skewness in the respective buffer-layer region (vice versa for the top wall).
