Environmental Engineering Reference
In-Depth Information
invasive PIV measurements were conducted to measure the flow patterns around the
artificial reef. On the basis of the numerical model validation, the flow fields of hollow cube
artificial reefs with different altitudes were analyzed using the numerical model. The effects
of spacing on the flow field around the parallel and vertical two hollow cube artificial reefs
were also analyzed in detail.
2. Numerical methods
Computational fluid dynamics (CFD) are generally used by engineers to solve fluid
dynamics problems that involve solving some form of the Navier-Stokes equations. The
numerical simulation analysis of flow fields around artificial reef is based on a dynamic, full
3D model elaborated with the aid of FLUENT 6.3 commercial code. The finite volume
method are used in the study to solve the three-dimensional Reynolds-averaged Navier-
Stokes (RANS) equations for incompressible flows.
2.1 Hypotheses
1.
Incompressible, viscous, Newtonian fluid for the water.
2.
Isothermal flows, regardless of heat exchange in the water.
3.
Flow is in the non-steady state.
4.
The water surface is modeled as a “moving wall” with zero shear force and the same
speed as the incoming fluid.
2.2 Hydrodynamic equations solved
The equations solved are the momentum equation, also known as the Navier-Stokes
equation, and the continuity equation. This approach is useful for solving laminar flows,
but, for turbulent flows, the direct solving of all the vortices in a turbulent flow is expensive.
Therefore, a model for turbulence must be added. There are several types of turbulence
models available. The most common are the RANS models and large eddy simulation
models. In the present study, the two-equation RANS models were chosen to resolve the
ensemble averaged flow and model the effect of the turbulent eddies. In the RANS
equations, various instantaneous physical parameters are replaced by the time-averaged
value. Incompressible flow is assumed such that the equations are as follows:
Momentum equation
∂
∂
P
∂
∂
u
i
'
'
ρ
(
uu
)
=−
+
(
μ
−
ρ
u u
)
+
S
(1)
ij
i j
i
∂
x
∂
x
∂
x
∂
x
j
i
j
j
Continuity equation
∂∂∂
++ =
∂∂ ∂
u
vw
xy z
0
(2)
For Eq. (1),
ρ
is the mass density;
u
i
is the average velocity component for x, y, z;
P
is a body
of fluid pressure on the micro-volume;
μ
is the viscosity;
u
′ is the fluctuation velocity; and
i
,
j
=1, 2, 3 (x, y, z).
S
i
is the source item.
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