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As deduced by Chapman and Kuhn [3], the damping function f-mu
must satisfy the near-wall limiting behavior . It is clear that
f-mu value should tend to unity in the fully turbulent zone,
while 0<f-mu<1 in the near wall region.This unbounded limiting
behavior of f-mu leads to a unrealistic situation f-mu>1 as grid
nodes being located very close to wall. Thus, the grid-
independence of computation mesh, particularly in the near wall
region of reattached flow, is usually difficult topursue, and it
sometimes aggravates the instability in the
computationaliteration process. The objective of this study is
to remove the unrealistic condition of f-mu>1 from the low-
Reynolds-number k-epsilon models when y<<1 . It is shown that
the Kolmogorov time scale is the smallest time scale in
turbulence. A criterion is thus set as f-mu=0 in the viscous
sublayer When the turbulent time scale being smaller than the
Kolmogorov time scale. Verification of the validity of the f-mu
functions associated with the criterion is implemented through
the test with a channel flow and a backward-facing step flow. It
is showed that the skin friction coefficient prediction can be
improved by introducing the criterion of f-mu function into the
calculations.The energy equation governing the thermal field is
re-derived. It reveals that the molecular Prandtl number, which
is shown in the conventional, Reynolds-averaged energy equation,
must be defined in terms of the constant-volume specific heat
capacity. With this correction, it is shown that the usual
overpredictions of the Nusselt number obtained with the energy
equation based on Pr_cp(in terms of the constant-pressure
specific heat capacity) can be significantly improved by the
energy equation based on Pr_cv (in terms of the constant-volume
specific heat capacity).
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