
Overview
The standard

model in
FLUENT is based on the Wilcox

model [
403], which incorporates modifications for lowReynoldsnumber
effects, compressibility, and shear flow spreading. The Wilcox model predicts
free shear flow spreading rates that are in close agreement with measurements
for far wakes, mixing layers, and plane, round, and radial jets, and is
thus applicable to wallbounded flows and free shear flows. A variation of
the standard

model called the SST

model is also available
in
FLUENT, and is described in Section
12.5.2.
The standard

model is an empirical model based on model transport
equations for the turbulence kinetic energy (
) and the specific dissipation
rate (
), which can also be thought of as the ratio of
to
[
403].
As the

model has been modified over the years, production terms
have been added to both the
and
equations, which have improved
the accuracy of the model for predicting free shear flows.
Transport Equations for the Standard

Model
The turbulence kinetic energy,
, and the specific dissipation rate,
, are obtained from the following transport equations:
Modeling the Effective Diffusivity
The effective diffusivities for the

model are given by
(12.53)  
(12.54) 
(12.55) 
LowReynoldsNumber Correction
The coefficient
damps the turbulent viscosity
causing a lowReynoldsnumber correction. It is given by
Modeling the Turbulence Production
Production of
The term
represents the production of turbulence kinetic energy. From the
exact equation for the transport of
, this term may be defined as
Production of
The production of
is given by
(12.513) 
Modeling the Turbulence Dissipation
Dissipation of
The dissipation of
is given by
(12.515) 
(12.517) 
Dissipation of
The dissipation of
is given by
(12.523) 
Compressibility Correction
The compressibility function,
, is given by
Model Constants