measurement is carried out at a depth of 0.2 h or 0.6
h (h = Depth), at 0.6 h it is carried out when the
flow depth is between 2.5-7.5cm (V = 0.6 h). And
the two-point method was carried out at a depth of
0.2 h and 0.8 h. The average flow velocity is
obtained by the formula (V= 0.5(0.2h+0.8h)), (7)
calculate the Froude number, (8) calculate the
Specific Energy for each type of narrowing, (9)
compare the results of the three forms of narrowing
type (h and Es) which is greater than the results of
the three forms of narrowing type.
b. Application of Specific Energy in Irrigation
Channel Design
(1) determine the discharge (according to the
variation of the discharge used in laboratory
testing), (2) determine the channel width before and
after narrowing (according to laboratory tests) for
each type of narrowing, (3) determine the elevation
of the upstream water table according to the results
of laboratory tests (h1), (4) calculate the discharge
per unit width (q) before and after constriction for
each type of narrowing, (5) calculate the Froude
number, (6) calculate the specific energy upstream,
(7) calculate the water level in the downstream
assuming upstream Es = downstream Es, (8)
compare the water level elevation (h2) laboratory
tests with other tests, (9) describe the results of the
analysis obtained.
2.2 Our Contribution
This paper present analyses the flow changes due to
the narrowing of the open channel. From previous
research, Cristian Auel et al. [1] discusses
Turbulence Characteristics in Supercritical Open
Channel Flows: Effects of Froude Number and
Aspect Ratio, Chieh Hsu et al. [2] discussing
Subcritical 90° Equal-Width Open-Channel
Dividing Flow, and Jhonson et al. [3] used abrupt
type of narrowing by using several different channel
widths, hence previous research has been used as a
benchmark in this study which used three types:
sudden narrowing type, transitional narrowing type,
and radius narrowing type with the same channel
width. Understanding the flow characteristics of a
narrowed channel is used to consider canals'
technical design, especially irrigation channels.
2.3 Open Channels
Channels that drain water with a free surface are
called open channels. Open channels can occur
considerably, ranging from ground-level flows
during rain until continuous water flow in the
prismatic channel. Channels are classified into two
types: natural existing and artificial channels.
Natural channels include all water channels
naturally occurring on earth, from small gutters in
the mountains, small rivers, and large rivers to river
mouths. Artificial channels are human-made
channels for specific purposes and interests.
Nature's hydraulic properties are very uncertain.
Artificial channels have a regular cross-section and
are easier to analyse than natural channels. Artificial
channels include roadside drainage, irrigation canals
to irrigate rice fields, sewers, drains to carry water
to hydroelectric power, drinking water supply
channels, floodway. In some ways, it can be
assumed that the approach is sufficiently consistent
with actual observations. Thus, the flow
requirements of this channel are acceptable for the
completion of theoretical hydraulics analysis.
2.4 System Classification
The open channel flow can be classified into several
types and described in various ways as follows. The
flow-through constriction can be supercritical or
subcritical. Critical depth can be formulated by
Rangga Raju [5].
2.4.1 Steady Flow And Unsteady Flow
A flow in an open channel is steady when variables
of flow (such as velocity V, pressure P, mass
density ρ, flow face A, debit Q) and so on, across
the point of the liquid, do not change with time. The
flow is said to be unstable (unsteady) if the flow
variable at each point changes with time. Most open
channel problems generally require only research on
flow behavior in steady-state. The equation
expresses debit Q on a channel cross-section for any
flow:
Q=VA (4)
With V = average velocity and A = The cross-
sectional area is perpendicular to the flow direction.
Most steady-flow problems, based on consideration,
are assumed to remain along a large section of the
channel, in other words, a steady flow of continuous
steady flow, from equation (4):
2.4.2 Critical and Supercritical Flow
The Stream is critical if the Froude number (F) is
equal to one (1), whereas the subcritical flow is
sometimes called (tranquil flow) when F < 1 and
supercritical or (rapid flow) when F > 1. The flow
velocity ratio with the force of gravity (per unit
volume) is known as the Froude number and can be
formulated as follows [6] so that F can be written as
Boris.A [7], Ven Te Chow [8], Osman Akan [9]:
=
(5)
WSEAS TRANSACTIONS on APPLIED and THEORETICAL MECHANICS
DOI: 10.37394/232011.2022.17.6
Ratna Musa,
Triffandy M. W., Amalia Rusaldy