California State University, Sacramento                                                                   CE135 Hydraulics Laboratory
Department of Civil Engineering                                                                                                   Instructor     MEH

For general information go to the Background Presentation

HYDRAULIC JUMP & DROP OFF – PROCEDURES


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

Objectives:
Observe and measure the major characteristics of the hydraulic jump.
Determine the relationships of
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. 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.]


SUMMARY

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 ()h/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 .

    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:
    Attach your sketch of the experimental set-up and copies of your input data and calculated results.
    Write out the key equations used in calculating the results, with one sample calculation for each equation.

Discussion Questions:
    Within the discussion section of your report, include discussion of 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?



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)     ________     ________     ________     ________      ________     ________