Geoscience Reference
In-Depth Information
Q
2
Secondary
Circulation
Dividing
Stream-surface
Boundary of
Separation Zone
Zone A
B
s
B
b
1
1
SECTION 2-2
SECTION 1-1
Zone C
2
Q
1
Zone B
Z
Z
U (Z)
Y
X
2
Fig. 2
The flow pattern in the intake entrance (Neary et al.
1999
)
Surface (DSS) or stream tube. As seen in Fig.
2
(Sect. 2.2), in the main channels
with rectangular section, the diversion flow width at the bed (
B
b
) is greater than that
in the surface (
B
s
), which causes the sediments entry into the intake, resulting from
their high density in the bed. The streamwise curvature in DSS yields imbalance
among the transverse pressure gradient, the centrifugal force, and shear force, as
a consequence of which a secondary current in clockwise direction is formed.
Such a secondary vortex is also formed along the main channel wall. The more
this current advances toward downstream, the more reduces its strength primarily
due to the fluid viscosity. The secondary current, besides the separation zone along
the inner wall of the branch channel (Zone A), gives rise to a complex three-
dimensional flow.
The extent of DSS in the main channel determines the rate of discharge to the
branch channel. The diversion flow width or stream tube at each surface (plan) is
defined as the distance from the main channel bank at the intake side to the stream
line ending in the stagnation point near the corner of downstream junction of the
intake and the main channel.
Taylor (
1944
) studied the flow in the 90
intake and proposed a graphical method
for determining the flow pattern. The method was used also by Thomson (
1949
)
for an analytical solution to the intake, though his assumptions based on the flow
depth to be constant is not practicable. Also Tanaka (
1957
) and Murota (
1958
),
assuming that the water depth in all channels is constant, analytically solved the
