HYDRAULICS ENGINEERING LAB MANUAL 1 2008-CIVIL-87 TABLE OF CONTENTS Experiment # 01 …………………………………………………………………….2 TO DETERMINE MANNING’S ROUGHNESS COEFFICIENT “n” AND CHEZY’S CO-EFFICIENT “C” IN A LABORTARY FLUME Experiment # 02 ……………………………………………………………………11 TO INVESTIGATE THE RELATIONSHIP BETWEEN SPECIFIC ENERGY (SE) AND DEPTH OF FLOW(Y) IN A LABORATORY FLUM Experiment # 03 ……………………………………………………………..........16 To study the flow characteristics over the hump or weir in a rectangular channel Experiment # 04 …………………………………………………………………...25 TO STUDY THE FLOW CHARACTERISTICS OF HYDRAULIC JUMP DEVELOPED IN LAB FLUME
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HYDRAULICS ENGINEERING LAB MANUAL
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TABLE OF CONTENTS
Experiment # 01 …………………………………………………………………….2
TO DETERMINE MANNING’S ROUGHNESS COEFFICIENT “n” AND CHEZY’S CO-EFFICIENT “C”
IN A LABORTARY FLUME
Experiment # 02 ……………………………………………………………………11
TO INVESTIGATE THE RELATIONSHIP BETWEEN SPECIFIC ENERGY (SE) AND DEPTH OF FLOW(Y) IN A LABORATORY FLUM
To study the flow characteristics over the hump or weir in a rectangular channel
Experiment # 04 …………………………………………………………………...25
TO STUDY THE FLOW CHARACTERISTICS OF HYDRAULIC JUMP DEVELOPED IN LAB FLUME
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EXPERIMENT NO. 1
TO DETERMINE MANNING’S ROUGHNESS COEFFICIENT “n” AND
CHEZY’S CO-EFFICIENT “C” IN A LABORTARY FLUME.
OBJECTIVE:
To study the variation in “n” with respect to discharge.
To study changes in “c” with respect to discharge.
To manipulate/investigate relation b/w: n” and “c”.
To learn the procedure of determining “n” and “c” of any existing channel.
APPARATUS:
S6 glass sided Tilting lab flume with manometric flow arrangement and slope adjusting scale.
Point gauge (For measuring depth of channel)
RELATED THEORY:
FLUME
Open channel generally supported on or above the ground.
UNIFORM FLOW:
A uniform flow is one in which flow parameters and channel parameters remain same with respect to
distance b/w two sections.
NON-UNIFORM FLOW:
A non-uniform flow is one in which flow parameters and channel parameters not remain same with
respect to distance b/w two sections.
STEADY FLOW: A steady flow is one in which the conditions (velocity, pressure and cross-section) may differ from point to point but DO NOT change with time.
UNSTEADY FLOW:
If at any point in the fluid, the conditions change with time, the flow is described as unsteady. (In practice there are always slight variations in velocity and pressure, but if the average values are constant, the flow is considered steady.
STEADY UNIFORMM FLOW:
Conditions do not change with position in the stream or with time. An example is the flow of water in a pipe of constant diameter at constant velocity.
STEADY NON-UNIFORMM FLOW:
Conditions change from point to point in the stream but do not change with time. An example is flow in a tapering pipe with constant velocity at the inlet - velocity will change as you move along the length of the pipe toward the exit.
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STEADY UNIFORMM FLOW:
At a given instant in time the conditions at every point are the same, but will change with time. An example is a pipe of constant diameter connected to a pump pumping at a constant rate which is then switched off.
UNSTEADY NON-UNIFORMM FLOW:
Every condition of the flow may change from point to point and with time at every point. For example
waves in a channel.
MANNINGS ROUGNESS FORMULA
The Manning formula states:
Where:
V is the cross-sectional average velocity (L/T; ft/s, m/s)
k is a conversion factor of 1.486 (ft/m)1/3 for U.S. customary units and 1 in SI Units.
n is the Manning coefficient (T/L1/3; s/m1/3)
Rh is the hydraulic radius (L; ft, m)
S is the slope of the water surface or the linear hydraulic head loss (L/L) (S = hf/L)
Manning formula is used to estimate flow in open channel situations where it is not practical to construct a weir or flume to measure flow with greater accuracy. The friction coefficients across weirs and orifices are less subjective than n along a natural (earthen, stone or vegetated) channel reach. Cross sectional area, as well as n', will likely vary along a natural channel. Accordingly, more error is expected in predicting flow by assuming a Manning's n, than by measuring flow across a constructed weirs, flumes or orifices.
HYDRAULICS RADIUS:
The hydraulic radius is a measure of channel flow efficiency.
Where:
Rh is the hydraulic radius,
A is the cross sectional area of flow ,
P is wetted perimeter .
The greater the hydraulic radius, the greater the efficiency of the channel and the less likely the river is to flood. For channels of a given width, the hydraulic radius is greater for the deeper channels.
The hydraulic radius is not half the hydraulic diameter as the name may suggest. It is a function of the shape of the pipe, channel, or river in which the water is flowing. In wide rectangular channels, the
hydraulic radius is approximated by the flow depth. The measure of a channel's efficiency (its ability to move water and sediment) is used by water engineers to assess the channel's capacity.
CHEZY’S FORMULA:
Chezy formula can be used to calculate mean flow velocity in conduits and is expressed as
v = c (R S) 1/2
Where v = mean velocity (m/s, ft/s) c = the Chezy roughness and conduit coefficient R = hydraulic radius of the conduit (m, ft) S = slope of the conduit (m/m, ft/ft)
PROCEDURE:
Measure Channel (Flume) width.
Adjust the suitable slope.
Fill the S-6 tilting flume up to some depth.
Note down the readings of differential manometer and see the corresponding discharge from
the discharge chart.
Note down the depth of flow at different points. (e.g. 2m,4m,6m)
Calculate the Co-efficient “C” and “n” accordingly by the given formulas.
PRECAUTIONS:
Take manometric reading only when flow is steady.
The height should not be measured near the joints or at points where there is turbulence in
flume.
The height measuring needle must be adjusted precisely.
The tip of the needle must be just touching the water surface while taking observations.
TO STUDY THE FLOW CHARACTERISTICS OVER THE HUMP OR
WEIR IN A RECTANGULAR CHANNEL
OBJECTIVE
To study the variation of flow with the introduction of different types of weirs in the flume.
APPARATUS
S6 tilting flume apparatus which consists of
Orifice
Differential manometer
Large chamber to study flow
Controlling meter to vary slope.
Hook gauge/point gauge to measure the depth
Broad crested weirs
Rounded corner weir
Sharp corner weir
RELATED THEORY
HUMP
Stream lined construction over the bed of a channel is called hump. OR The raised bed of the channel at a certain location is called as hump. WEIR
It is the streamlined wall or structure constructed across a river or a stream at a suitable location. It is commonly used to raise the water level at a river or stream to divert the required amount of water into an off taking canal. Weirs can be gated or ungated. Gated weir is called as BARRAGE
FLOW OVER WEIR OR HUMP
a) SUB CRITICAL FLOW
Consider a horizontal, frictionless rectangular channel of width B carrying a discharge Q at depth y1.
Let the flow be subcritical. At section 2, a smooth hump of height ΔZ is built on the floor. Since there are
no energy losses between sections 1 and 2, construction of a hump causes the specific energy at section
to decrease by ΔZ. Thus the specific energies at sections 1 and 2 are,
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E2 = E1 - ∆Z
Channel transition with a hump
Since the flow is subcritical, the water surface will drop due to a decrease in the specific energy.
In above Fig the water surface which was at P at section 1 will come down to point R at section 2. The
depth y2 will be give by,
b) SUPERCRITICAL FLOW
If Y1 is in the supercritical flow regime, Fig below shows that the depth of flow increases due to the
reduction of specific energy. Point P` corresponds to y1 and point R` to depth at the section 2. Up to the
critical depth, y2 increases to reach yc at ΔZ = ΔZmax. For ΔZ > ΔZmax , the depth over the hump y2 = yc will
remain constant and the upstream depth y1 will change. It will decrease to have a higher specific energy
E1`by increasing velocity V1.
Specific energy diagram
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EFFECT OF HUMP HEIGHT ON THE DEPTH OF FLOW:
Height of hump is less than critical hump height then there will be sub critical flow over the hump, downstream of the hump and upstream of the hump. Depth of flow over the hump will decrease by a certain amount as there is a slight depression in the water. Further increase in the height of hump will create more depression of water surface over the hump until finally the depth becomes equals to the critical depth. When the hump height will be equal to the critical depth then there will be critical flow over the hump, sub critical on the upstream side and super critical just downstream of the hump. If the hump is made still higher, critical depth will maintain over the hump and depth on upstream side will be increased. This phenomenon is referred to as damming action. Critical Hump Height is the minimum hump height that can cause the critical depth over the hump is called as critical hump height.
CASE 1 When Z < << Zc and y2 >>> yc
The flow conditions will be sub critical
Upstream level increases
Over hump y2 > yc
At downstream depth is recovered after a long distance
CASE 2 When Z = Zc
Upstream level increases
Over hump y2 = yc
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CASE 3 When Z > Zc
Afflux on upstream side (damming action)
y1 > y3 and y2 = yc
At this stage E1 = y1 + v12/2g + afflux
DAMMING ACTION: It is the sudden increase of the water depth at upstream side due to increase in hump height.
PROCEDURE:
1. Fix the slope of the flume 2. Introduce a round corner wide crested weir in the flume at certain location 3. Set the discharge in the flume having certain value. 4. Note depth of flow at upstream side of hump, over the hump and downstream side of hump at
certain point. 5. Repeat steps 2-4 for the other discharges 6. Repeat the same procedure for sharp cornered wide crest weir 7. Predict the type of flow at every section 8. Compare depths with critical depth for every discharge value and report the type of flow. 9. Draw flow profile over the hump for both types of humps.
PRECAUTIONS:
Take manometric reading only when flow is steady.
The height should not be measured near the joints or at points where there is turbulence in flume.
The height measuring needle must be adjusted precisely.
The tip of the needle must be just touching the water surface while taking observations.
0.006323 35.64 172 172 171 171.67 162 150 140 150.67 11 19 24 18.00 Sub Critical Sub
Critical Super
Critical
2 0.01058 50.24 189 190 188 189.00 177 161 142 160.00 12 22 32.5 22.17 Sub Critical Sub
Critical Super
Critical
3 0.013263 58.41 202 202 200 201.33 190 169 152 170.33 23 25 37 28.33 Sub Critical Sub
Critical Super
Critical
4
SHARP CORNER
WEIR
0.008488 43.37 120 121 120 120.33 115 97 92 101.33 19 23 23 21.67 Sub Critical Sub
Critical Super
Critical
5 0.011659 53.60 134 135 133 134.00 127 100 99 108.67 20 30 39 29.67 Sub Critical Sub
Critical Super
Critical
6 0.015228 64.04 148 149 148 148.33 140 108 106 118.00 30 37 44 37.00 Sub Critical Sub
Critical Super
Critical
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SURFACE WATER PROFILES:
Round Corner Broad Crested Weir:
0
0.05
0.1
0.15
0.2
0.25
0 1 2 3 4 5 6 7 8
WA
TER
DEP
TH (
m)
HORIZONTAL DISTANCE (m)
Q = .006323 m3/s
0
0.05
0.1
0.15
0.2
0.25
0 1 2 3 4 5 6 7 8
WA
TER
DEP
TH (
m)
HORIZONTAL DISTANCE (m)
Q = .01053m3/s
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Sharp Corner Broad Crested Weir:
0
0.05
0.1
0.15
0.2
0.25
0 1 2 3 4 5 6 7 8
WA
TER
DEP
TH (
m)
HORIZONTAL DISTANCE (m)
Q = .0.013263m3/s
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0 1 2 3 4 5 6 7 8
WA
TER
DEP
TH (
m)
HORIZONTAL DISTANCE (m)
Q = 0.008488m3/s
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0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0 1 2 3 4 5 6 7 8
WA
TER
DEP
TH (
m)
HORIZONTAL DISTANCE (m)
Q = 0.011659m3/s
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 1 2 3 4 5 6 7 8
WA
TER
DEP
TH (
m)
HORIZONTAL DISTANCE (m)
Q = 0.015228 m3/s
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RESULTS:
The Flow is sub Critical at upstream in both cases.
The Flow is subcritical over weir in both cases.
The Flow in all of the above cases is Supercritical at the downstream side immediately after the weir.
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EEXXPPEERRIIMMEENNTT ## 0044
TO STUDY THE FLOW CHARACTERISTICS OF HYDRAULIC JUMP
DEVELOPED IN LAB FLUME
OBJECTIVES
1. To physically achieve the hydraulic jump in lab flume.
2. To measure the physical dimensions of hydraulic jump.
3. To calculate the energy loses through hydraulic jump.
4. To plot water surface profiles of the hydraulic jump for various discharges.
APPARATUS
S-6 tilting lab flume with
Manometer
Flow arrangement
Slope adjusting scale
Hook gauge
RELATED THEORY
HYDRAULIC JUMP
The rise of water level which takes place due to transformation of super critical flow to sub critical flow
is termed as hydraulic jump.
PRACTICAL APPLICATIONS OF HYDRAULIC JUMP
To dissipate the energy of water flowing over the hydraulic structures and thus preventing scouring (vertical erosion) downstream of structures.
To recover head or raise the water level on the downstream of a hydraulic structure and thus to maintain high water level in the channel for irrigation or other water distribution purposes.
To increase the weight of apron and thus reduce uplift pressure under the structure by raising water depth on the apron. Apron: Layer of flexible material provided on the downstream floor. It act as an inverted filter.
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To mix chemicals used for water filtration etc.
EXPRESSION FOR DEPTH OF HYDRAULIC JUMP
From the figure below. Depth of hydraulic jump =
We can find d2 , for known value of d1 , by using expression,
EXPRESSION FOR LOSS OF ENERGY DUE TO HYDRAULIC JUMP
On simplifying, we can find head loss for known values of d1 and d2 ,
LENGTH OF HYDRAULIC JUMP
The length between two sections where one section is taken just before the hydraulic jump and second
section is taken just after the hydraulic jump is termed as length of hydraulic jump.
Approximate length of hydraulic jump = 5 -7 times depth of hydraulic jump
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LOCATIONOF HYDRAULIC JUMP
Location of hydraulic jump is governed by two factors,
I) d2 (Depth of flow just after the hydraulic jump)
II) Y2 (Normal depth of flow on downstream side of hydraulic structure)
CASE – 01 When d2 < Y2
In Case – 01, Hydraulic jump will be formed over the glaces of hydraulic structure as shown in the figure
and it will be weak jump/Submerged jump.
CASE – 02 When d2 = Y2
In Case – 02, Hydraulic jump will be formed on the toe of hydraulic structure as shown in the figure and
it will be a relatively strong jump than Case - 01.
U/S D/S
y2
Crest
d2
U/S D/S y2
Crest
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CASE – 03 When d2 > Y2
In Case – 03, Hydraulic jump will be formed ahead of hydraulic structure as shown in the fig. And it will
be a relatively strong jump as compared to Case – 01 and Case – 02.
Comparatively, Case – 02 is ideal case with sufficient energy dissipation and structure will also be safe
(because jump will be formed at the toe of structure).
CLASSIFICATION OF HYDRAULIC JUMP
Type of hydraulic jump is defined based on Froude’s number,
i) FN = 1.0 No jump
ii) FN = 1.0 – 1.7 Undulated jump/Roller type jump
iii) FN = 1.7 – 2.5 Weak jump
iv) FN = 2.5 – 4.5 Oscillating jump
v) FN = 4.5 – 9.0 Steady jump
vi) FN > 9.0 Strong jump
y2 d2 U/S
D/S
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PROCEDURE
Adjust the S-6 Tilting flume at a slope and check if there is any problem in arrangement or
anything residual inside the flume causing obstruction in flow.
Setup a specific discharge in the flume.
Note down the depth of the water surface before, after and at the hydraulic jump.
Repeat the above procedure with by increasing discharge.
Complete the table of observations and calculations and plot the water surface profile for all
discharges.
PRECAUTIONS
The height should not be measured near the joints or at points where there is turbulence in
flume.
The height measuring needle must be adjusted precisely.
The tip of the needle must be just touching the water surface while taking observations.
The reading measurement at the hydraulic jump is difficult, so note the flow carefully and take