3.4.2.1.2 Turbulence modeling
Fluid flow is governed by basic conservation principles
such as conservation of mass, momentum and energy.
All these conservation principles are solved according to
a fluid model given by a set of partial differential equations,
representing the governing equations of the fluid
motion.
Turbulent flow is a type of fluid flow characterized by
fluctuating and chaotic property changes.
In this work, the RANS (Reynolds Averaged Navier-
Stokes) approach is used to model the effects of turbulence.
A two-equation RANS-turbulence model is used
as it offers a good compromise between numerical effort
and computational accuracy. The so-called velocity scale
and length scale are solved using separate transport
equations – hence the term “two equation model”. This
model holds two transport equations, one for turbulent
kinetic energy (k) from which the turbulence velocity
scale is computed, and one for turbulent dissipation rate
(ε), therefore the name k-ε model [5].
For the standard k-ε turbulence model, the turbulence
parameters are also to be specified at the inlet boundary.
k value calculation [4] (Ansys, 2010a)
k = 3/2*(inflow velocity * turbulent intensity)2 =3.75*10-5
= 3/2*(0.1*0.05)2 =3.75*10-5, where the turbulent intensity
is set to 0.05
Eddy length scale calculation [4] (Ansys, 2010a)
Eddy length scale,(l)= 0.07* characteristic length
The characteristic length for our model is 10m, hence
l = 0.07*10 = 0.7
The turbulence parameters are summarized in Table 3.7.