Geoscience Reference
In-Depth Information
channel 1
channel 2
channel 3
channel 4
5
135
°
90
°
45
°
(h = 2)
(h = 2)
(h = 2)
(h = 2)
20
20
10
20
10
20
10
Fig. 1 Channel geometries (dimensions in meters)
geometrical parameters for all the channels are as follows: main channel width of
20 m and length of 80 m, diverting channel width of 5 m, and the water depth of 2 m.
The grid (86,428 cells) is made in curvilinear body-fitted coordinates in which
the grid lines are determined by a coordinate system that conforms to the geometric
boundary of model. The largest variations in the fluid flow, sediment transport, and
turbulence occur in the region of the bifurcation and in the boundary layer, so grid
refinement is applied in these regions.
For all computations, the following flow parameters are set: density of water
r ¼
1,000 kgm
3;
wall roughness
k
s
¼
2,650
kgs
1
. The inflow discharge is 30 m
3
s
1
. At the inlet, a uniform flow profile is
defined:
u
(
z
)
0.003 m; and sediment density
r
s
¼
0.75 ms
1
. The turbulent kinetic energy profile at the inlet is
approximated by a linear function:
k
(
z
)
¼
u
*
2
c
m
0.5
and
¼
k
0
(1
z
/
h
), where
k
0
¼
t
w
r
1
)
0.5
, in which
c
m
¼
u
*
¼
(
empirical constant in k-
e
model (
c
m
¼
0.09),
h
¼
flow depth (m),
k
0
¼
turbulent kinetic energy above the wall boundary layer
(m
2
/s
2
),
u
*
¼
wall shear stress velocity (ms
1
),
z
¼
vertical coordinate (m), and
wall shear stress (N/m
2
) (Rodi
1993
). The dissipation rate profile is approxi-
mated by the equation
t
w
¼
u
*
3
/
(
z
b
)
z
b
/
z
(1
z
/
h
), where
e
(
z
)
¼
k
z
b
, in which
e
(
z
)
¼ e
k ¼
von Karman's constant,
z
b
¼
reference level at the bed (equal to the vertical
coordinate of the first computational cell;
z
b
¼
0.046 m).
For channel 1, one flow computation is carried out, whereas for each of the
channels with bifurcation, two discharge ratios are chosen with the following
discharges and flow velocities in the branches:
30 m
3
s
1
5m
3
s
1
500 ms
1
Q
¼
Q
1
¼
¼>
u
1
¼
0
:
ð
branch
Þ
25m
3
s
1
625 ms
1
Q
2
¼
¼>
u
2
¼
0
:
ð
main
Þ
30 m
3
s
1
10m
3
s
1
000 ms
1
Q
¼
Q
1
¼
¼>
u
1
¼
1
:
ð
branch
Þ
20m
3
s
1
500 ms
1
Q
2
¼
¼>
u
2
¼
0
:
ð
main
Þ
