Description
Please complete all 5 requirements from the data analysis and di
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Spring’22
CGN 3021 L
University of South Florida
E4: HYDRAULIC JUMP IN FLUME
Learning Objectives
Observe the hydraulic jump downstream of hydraulic structures such as a sluice gate in
an open channel flume
Compare observed and theoretical ratios of upstream and downstream depths.
Quantify the energy lost due to a hydraulic jump.
Theory of the Experiment
In engineering practice, the hydraulic jump frequently appears downstream from overflow
structures (spillways) or underflow structures (sluice gates) where velocities are high. The
hydraulic jump is a rapid transition from supercritical flow to subcritical flow. It is formed when
liquid at high velocity discharges into a zone of lower velocity, creating a rather abrupt rise in the
liquid surface (a standing wave) accompanied by violent turbulence, eddying, air entrainment, and
surface undulations The transition is generally a turbulent process with a significant energy
loss(∆E), that cannot be neglected. A hydraulic jump is commonly used to dissipate energy, and
reduce the downstream velocity. Figure 1 shows the variables included in a hydraulic jump.
EGL
E
2
V1 /2g
Jump
V22/2g
Flow
Figure 1: Hydraulic Jump Illustration
A flow is supercritical when:
Where, Fr is the Froude number, V is the fluid velocity, g is the gravitational constant, and y is
fluid depth.
For a channel of rectangular cross-section and constant width:
University of South Florida
CGN 3021 L
Spring’22
Where q=Q/b, the flow rate per unit width of the channel.
In supercritical flow, disturbances travel downstream, and upstream water levels are unaffected
by downstream control. Supercritical flows are characterized by high velocity and small flow depth
and are also known as shooting flows.
A flow is subcritical when:
In subcritical flow, disturbances travel upstream as upstream water levels are affected by downstream
control. Subcritical flows are characterized by low velocity and large flow depth and are also known as
tranquil flows. In a hydraulic jump, supercritical flow changes to subcritical flow over a short horizontal
distance.
In horizontal rectangular channels, the relationship between the downstream and upstream depths of a
hydraulic jump is given by the following equation:
where,
y1 = upstream depth of jump (m)
y2= downstream depth of jump (m)
F1 = Froude number for upstream flow
In addition, the critical depth of a rectangular channel can be calculated as follows:
Where, q is the flowrate per unit width (Q/b) ( 2 /s). This critical depth can be used to
characterize whether a flow is subcritical (y>yc) or supercritical (y 9.0
Energy dissipation
< 5%
5 – 15%
15 – 45%
45 – 70%
70 – 85%
Experimental Procedures
A sluice gate is installed in the flume used to generate the hydraulic jump. The flume should be
leveled. The sluice gate will create a supercritical flow immediately after the gate, followed by
a hydraulic jump, and then a subcritical flow downstream of the hydraulic jump. Clamp the
sluice gate assembly securely to the sides of the channels close to the upstream end of the flume
with sharp edge on the bottom of the gate facing upstream. For accurate results, the gaps between
the gate and channel should be sealed on the upstream side using Plasticine.
One level gauge is located upstream of the hydraulic jump to measure the supercritical depth,
y1, and the other downstream of the hydraulic jump to measure the subcritical depth, y2. The
gauges are zeroed with the bed of the channel and have to be moved depending on the location
of the hydraulic jump. Measure the accurate flowrate, the upstream depth and the downstream
depth.
Steps
1. Adjust the knob on top to position the sharp edge of the gate 0.015m above the bed of the
flume. Place one stop log at the discharge end of the flume.
2. Gradually open the flow control valve and adjust the flow until an undular jump is created
with small rippled decaying towards the discharge end of the flume. Observe and sketch
flow pattern.
3. Increase the height of water upstream of the gate by increasing the flowrate and increase
the height of the stop logs to create a hydraulic jump in the center of the working section.
Observe and sketch the flow pattern.
4. Move one level gauge to the region of rapid flow just upstream of the jump. Move the
second level gauge to the region of tranquil flow just after the jump. Measure and record
the values of y1, y2, and Q.
5. For each sluice gate opening, collect data for 4 different flow rates.
6. Repeat steps 1 through 5 for a sluice gate opening of 0.020m .
University of South Florida
CGN 3021 L
Spring’22
Data Analysis and Discussions
1. Calculate the Froude numbers for the upstream depth y1 (F1) and downstream depth y2
(F2)
a. Do you see a transition from supercritical depth to subcritical depth?
b. Classify the type of jump based on the upstream Froude number.
2. Calculate the critical depth (yc) for all flow rates.
a. Check whether your subcritical depths are greater than critical depths and your
supercritical depths are less than your critical depths.
3. Calculate the theoretical downstream depth, 2′ using the measured upstream depth (y1).
Plot 2′ /y1 vs y2/y1 on graph. Do the measured and theoretical downstream depths
match?
4. Calculate the loss of energy (E). For each gate opening, plot the energy losses (E) in the
jump as a function of flow rate (Q). How does energy loss change with flow rate?
5. Suggest an application where the loss of energy in hydraulic jump would be desirable.
How is the energy dissipated?
University of South Florida
Spring’22
CGN 3021 L
Data Sheet
Breadth of gate, b = ………. (m)
Table 2: Hydraulic Jump Experiment Data and Results
Experimental Data
Volume of
Gate
Upstream Downstream
water
depth,
depth,
Trial opening,
collected
in tank,
(m) y1 (m)
y2 (m)
V (L)
1
2
3
4
5
6
7
8
Calculated Data
Time to
collect
volume
of water,
t (s)
Q
( 3 /s)
F1
F2
yc
2′
(m)
(m)
E
(m)
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