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FLOW CHARACTERISTICS OF SEMI CIRCULAR CONTRACTION CRITICAL FLOW FLUMES FOR LOW DISCHARGES UNDER DIFFERENT SUBMERGENCE CONDITIONS

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Title FLOW CHARACTERISTICS OF SEMI CIRCULAR CONTRACTION CRITICAL FLOW FLUMES FOR LOW DISCHARGES UNDER DIFFERENT SUBMERGENCE CONDITIONS
 
Creator KRUPAVATHI, K
 
Contributor SATYANARAYANA, T.V
 
Subject FLOW, CHARACTERISTICS, SEMI, CIRCULAR, CONTRACTION, CRITICAL, FLOW, FLUMES, LOW, DISCHARGES, DIFFERENT, SUBMERGENCE, CONDITIONS
 
Description The rapidly increasing use of all available water resources and the increasing
costs of on-farm irrigation development require economical use of irrigation water.
The irrigated agriculture sector has been the largest user of water in the recent times.
Efficient water management in irrigated agriculture requires accurate measurement
and application of water. Since the present rate of development of water resources is
not enough to meet the requirements of increasing population, any improvement in
the efficiency of utilization of existing water resources acquires greater importance.
Measurements of irrigation water flows in field channels have usually been
expensive, too often of questionable accuracy and otherwise difficult to apply to
field situations. The techniques available in open channel hydrometry are the use of
hydraulic structures (devices), velocity-area methods, dilution techniques and slopehydraulic
radius and area methods. Considering the constraints in the measurements
of low discharges in open channels, hydraulic structure technique is best suited. Most of the research has been concentrated on the parallel critical flow broad
crested weirs involving the bottom contracted sills. But the social acceptability of
these by the farmers under Indian conditions has been very low with the
apprehension that the flow retardation exists in the channel leading to reduction in
the flow through the weir due to raised channel bottom. Similarly, most existing
flow measuring devices involving side contractions have been relatively expensive
to maintain and difficult to install or costly to construct. The difficulty in the
analysis of curvilinear flow, the complication in fabrication, the errors in
installation, the economy and the sensitivity towards submergence have limited the
use of these flumes.
Although some research work has been done on side contraction flumes, a
limited study appears to have been made along these lines for the side contracted
flumes of rectangular cross section. A laboratory experiment entitled “Flow
Characteristics of Semi Circular Contraction Critical Flow Flumes for Low
Discharges under Different Submergence Conditions” was conducted in a hydraulic
flume with motorized bed slope alteration facility at the Hydraulics laboratory,
College of Agricultural Engineering, Bapatla to study the effect of percentage of
contraction and submergence on flow characteristics like critical depth, location of
critical depth, accuracy of measurement and total quantity of material used etc. The
experiment consisted of three different contractions (20%, 40% and 60%) tested
with three different discharges (10 ls-1, 14 ls-1 and 18 ls-1) and four submergence
levels (60%, 70%, 80% and 90%).
The concept of circular flume combined with the traditional cutthroat flume
to achieve both simplicity and accuracy of the circular flume and the non-obstructive
advantage of traditional cutthroat flume (Samani and Magallanez (2000) is adopted
in the present study. The Flume was constructed by placing two semicircular
cylinders attached to the side walls of the rectangular channel portion of the
hydraulic flume. The submergence conditions are created by two gates placed at
starting and end of the hydraulic flume.
The semi circular contraction flume-1 is fixed to the side walls of hydraulic
flume. At 10 ls-1 discharge, starting with the free flow condition, the submergence
condition has been increased gradually to 60% submergence, 70% submergence,
80% submergence and 90% submergence with the help of tail gate provided at the
end of the flume. The process of recording the water surface profiles has been
repeated with remaining two discharges of 14 ls-1 and 18 ls-1 and four different
submergence conditions for each flume type. The semi circular contraction flume-1
has been replaced by flume-2 and flume-3 subsequently. Again water surface
profiles for discharges of 10 ls-1, 14 ls-1 and 18 ls-1 and for submergence conditions
60%, 70%, 80% and 90% have been noted as in the previous run.
The method of repeating variables is used in deriving an expression (Eq. 4.1)
for predicting the discharge and is also cross checked with Buckingham pi theorem.
The generalized discharge and end depth relationship (Eq. 4.2) is also used to predict
the theoretical discharges. For a given contraction, the constants in Eq. 4.1 and Eq.
4.2 are predicted based on least square method of curve fitting.
Critical depth for flume-1 with 20% contraction doesn’t occur in the throat
section for all discharges at 90% submergence conditions (free flow condition),
because critical flow conditions are not created with 20% contraction in throat
section. The location of critical depth moved towards the end of the flume at all
discharges in case of flume-2 and flume-3 with increase in submergence levels up to
80% submergence. The location of critical depth moved towards the center of the
flume at all discharges with increase in contraction from 40% to 60%. With the
highest submergence condition of 90% , the location of critical depth is not found in
the throat section at all discharges for all flumes indicating that the side contracted
flumes are sensitive to higher submergence conditions.
The deviation of discharge under free flow conditions depicted from Eq.4.1
and Eq. 4.2 are within the range of ± 5% of actual discharge for all flumes. A single
measurement of end depth in semi circular contraction critical flow flumes can be
used for discharge computation in open channels, if the submergence conditions are
below 80% in general. The fabrication costs of semi circular contraction flume-1,
flume-2 and flume-3 are Rs. 2250.00, 2650.00 and 3050.00 respectively. The flumes
can be easily fabricated and installed in field channels of farmers fields to measure
water.
 
Date 2016-07-30T15:18:41Z
2016-07-30T15:18:41Z
2008
 
Type Thesis
 
Identifier http://krishikosh.egranth.ac.in/handle/1/70338
 
Language en
 
Relation D8351;
 
Format application/pdf
 
Publisher ACHARYA N. G. RANGA AGRICULTURAL UNIVERSITY, RAJENDRANAGAR, HYDERABAD