Abstract
Compressible turbulent plane Couette flows are studied via direct numerical simulation for wall Reynolds numbers up to
$Re_w=10\ 000$
and wall Mach numbers up to
$M_w=5$
. Various turbulence statistics are compared with their incompressible counterparts at comparable semilocal Reynolds numbers
$Re^*_{\tau,c}$
. The skin friction coefficient
$C_f$
, which decreases with
$Re_w$
, only weakly depends on
$M_w$
. On the other hand, the thermodynamic properties (mean temperature, density and others) strongly vary with
$M_w$
. Under proper scaling transformations, the mean velocity profiles for the compressible and incompressible cases collapse well and show a logarithmic region with the Kárman constant
$\kappa =0.41$
. Compared with wall units, the semilocal units yield a better collapse for the profiles of the Reynolds stresses. While the wall-normal and spanwise Reynolds stress components slightly decrease in the near-wall region, the inner peak of the streamwise component notably increases with increasing
$M_w$
– indicating that flow becomes more anisotropic when compressible. In addition, the near-wall turbulence production decreases as
$M_w$
increases – due to rapid wall-normal changes of viscosity caused by viscous heating. The streamwise and spanwise energy spectra show that the length scale of near-wall coherent structures does not vary with
$M_w$
in semilocal units. Consistent with those in incompressible flows, the superstructures (the large-scale streamwise rollers) with a typical spanwise scale of
$\lambda _z/h\approx 1.5{\rm \pi}$
become stronger with increasing
$Re_w$
. For the highest
$Re_w$
studied, they contribute about
$40\,\%$
of the Reynolds shear stress at the channel centre. Interestingly, flow visualization and correlation analysis show that the streamwise coherence of these structures degrades with increasing
$M_w$
. In addition, at comparable
$Re^*_{\tau,c}$
, the amplitude modulation of these structures on the near-wall small scales is quite similar between incompressible and compressible cases – but much stronger than that in plane Poiseuille flows.
Publisher
Cambridge University Press (CUP)
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics,Applied Mathematics
Cited by
3 articles.
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