| Summary: | Rivers in Indonesia is meanders, especially in downstream section that flow
through residential and industrial areas. River bank erosion is often being found
on the outer side and sedimentation at the inner side of the bend. Meanwhile, the
theory used for river bank protection structure design is still base on flow in a
straight channel. The characteristics of flow in the curve channel are much
different than that in a straight channel. The existence of centrifugal force causes
an increase in secondary flow, which affects flow characteristics changes,
including the characteristics of turbulence.
To understand the changes in the flow and turbulence characteristics, it
conducted a research using a 180� open channel bend, 50 cm wide and 40 cm
high. Bed materials such as sand are used, with median diameter, d50: 1 mm and
mass density of 2.67 g/cm3. The bed material in the approach flow is critical with
a 15.9 cm depth. After continuous running for 30 hours, it obtained stable bed
topography. MicroADV 16MHz is used to measure the three-dimensional velocity
with a frequency of 50 data per second.
The results show that the path of maximum scour occurs in the middle of the
channel and shifted to the outside of the bend in the outlet area. Maximum
sediment along the curved channel occurs in the inside of the bend. While the path
of maximum scour on the side of the entrance tend to approach the next turn then
shifts to the center and close to the bottom line, then shifted again to the outer side
of the bend in the outlet of the bend. Reynolds stress component on tangential
direction is negative on the outer side of the entrance area and on the inner side at
the � = 90 � to outlet of the bend. While the positive Reynolds stress occurs on the
outer bank at the ï�± = 90ï�° to 180ï�°ï� bend angle. Due to the changes in the flow
characteristics, the vertical distribution of turbulent intensity in the curved channel
has not followed the exponential equation of Nezu (1977). Meanwhile, the ratio of
tangential and radial turbulent intensity is distributed following an exponential
equation. Changes in flow characteristics in curved channels also affect the value
and distribution of turbulent kinetic energy. If the straight flow, the location of the
maximum turbulent kinetic energy is near the bed, then in the curved channel �� =
90 � -120 ��, it is located near the water surface. In general, turbulent parameters:
Reynolds stress, turbulent intensity and turbulent kinetic energy near the bed on
the flat-bed are greater than at the eroded-bed curved channel. Furthermore, the
application Clauser method and Reynolds stress distribution method to determine
the shear velocity in the curved channel shows that the Clauser method produces
greater shear velocity values with a mean difference of 20.693%.
Key words: Reynolds stress, turbulence kinetic energy, shear velocity, curved
channel
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