Calif. State Univ., Sacramento CE135 Hydraulics Lab
Dept of Civil Engineering Instructor MEH
HYDRAULIC JUMP & DROP OFF
OBJECTIVES:
From experimental data, determine the following relationships:
Y2/Y1 (sequent depth/initial depth) vs. F1
(Froude number @ initial depth)
E/Y1 (energy loss/initial depth) vs. F1
L/Y2 (length of hydraulic jump vs. sequent depth)
vs. F1
Measure the shape of flow as it drops off the end of the channel
APPARATUS:
One-half meter glass-walled flume with sluice gates
Point gage and manometer board with piezometer taps
PROCEDURE:
Set up experiment
- Close the drain valve on the head tank.
- Take the zero datum readings for point gages and manometers.
- Open the surge tank valve and turn on the large pump.
Conjugate depth and length measurements for a range of Froude numbers
- Measure the water surface levels at the initial and sequent depths by point gage readings.
- Measure the length of the jump within the flow reach with turbulent air bubbles.
- Record the flow rate
- Repeat at different Froude numbers by adjusting either the flow rate or
the sluice gate opening.
Make sure that your Froude numbers will reasonably cover the rage between 1 to 10.
Profile for a Channel Drop-off at a single flow rate of about 600 gpm
- Open both sluice gates so the flow drops off the end of the channel.
- Record the flow rate
- Measure the height of water with the point gage at several points along the water surface
Note: The distance between points
should increase as you move away from the drop-off site
Open the head tank drain valve and shut off the flow
HYDRAULIC JUMP & DROP-OFF – RESULTS
Format: Memo Report
(Include your team logo somewhere in the report.)
Present the key results and describe any major deviations from the printed procedures and why you did them.
You do not need to turn in the lab procedure sheet with your report, but it is ok to add it as an attachment. You may use a computer sketch of the apparatus in the body of the report, but the attachment must be hand drawn.
RESULTS:
Plot the ratio of initial and sequent depths (Y2/Y1) of the hydraulic jumps vs. the Froude number
@ initial depth F1 for both experimental and theoretical curves. Comment on how well your
experimental curve compare to the theoretical curve.
Plot the ratio of head loss and initial depth (Δh/Y1) vs. Froude number F1 for both experimental
and theoretical curves. Comment on how well your curve compares to the theoretical curve.
Plot the ratio of hydraulic jump length and sequent depth (L/Y2) vs. Froude number F1.
Compare your plotted curve with USBR’s empirical curve .
Discussion Questions:
Within your discussion of results, include the following issues:
Why do engineers purposely create a hydraulic jump just downstream of a spillway?
Why it is essential for an engineer to know the exact location of the hydraulic jump?
Plot the water surface profile by point gage readings for the section approaching the end of the
channel. How does the depth compare with the critical depth level for flow at the rate used
for the drop-off run?
ATTACHMENTS:
Sketches: Note the hydraulic jump & drop off are seperate items
Write out the key equations used in calculating the results, with one sample calculation for each equation.
I recommend including copies of your input data and calculations of results.
References:
Brater, E.F. & H.W. King, 1976, Handbook of Hydraulics, 6th ed., McGraw-Hill Inc.
Roberson, J.A.. & Crow, C.T., 1997, Engineering Fluid Mechanics, 6th ed., John Wiley and Sons, Ch 15
Calif. State Univ., Sacramento CE135 Hydraulics Lab
Dept of Civil Engineering Instructor MEH
HYDRAULIC JUMP IN RECTANGULAR CHANNEL
INPUT (OBSERVED) DATA
Lab. Team Name: Date of Experiment:
Student Names:
CONSTANT DATA
Water Temperature ________° F Rectangular Flume Width ________ ft
Point Gage Readings at Bottom: Before Gate ________ ft After Gate: ________ ft
HYDRAULIC JUMPS AT VARYING FLOWS
Run Flow Rate Before Gate Before Jump After Jump Length of Jump |
No. (gpm) --------------------------- feet ---------------------------------
1
2
3
4
5
6
7
SURFACE PROFILE APPROACHING CHANNEL DROP-OFF
Data for Q = _________ gpm
X = Distance From End of Channel Y = Point Gage Reading at Water Surface
X (Ft) ________ ________ ________ ________ ________ _________
Y (Ft) ________ ________ ________ ________ ________ ________