7.10 Specific dissipation rate
The model is one of a family of two-equation models for turbulence.
With two equations, the models can represent each of the scales,
and
, which characterise
. Most often,
is
used to represent
.
The other variable must represent and so far we have
used
with SI units
. The specific dissipation rate
, with SI units
of
, is a popular alternative for this variable in turbulence
modelling.
While Kolmogorov first proposed a two-equation
model,15
the
models used in CFD originate from Wilcox.16
Here, “models” is plural since there are several versions of
model with modifications and additions from its original form.
The original model is
presented below (with some changes to the original variable names),
assuming
= constant for direct comparison with
in
Sec. 7.1
.
![]() |
(7.36) |
![]() |
(7.37) |
The standard model coefficients are
![]() |
(7.38) |

![]() |
(7.39) |

![]() |
(7.40) |


With wall functions, the boundary condition applied to
set a near-wall cell value
according to
![]() |
(7.41) |


![]() |
(7.42) |




