Demonstration of Hydraulic Jump

Introduction:


A hydraulic jump is a steplike increase in fluid depth in an open channel. It is a rapid transition from supercritical flow to subcritical flow. The transition is generally a turbulent process with a significant energy loss(βˆ†E) that cannot be neglected. A hydraulic jump is commonly used to dissipate energy and reduce the downstream velocity.

Hydraulic Jump
Hydraulic jump geometry

A hydraulic jump is formed when liquid at high velocity discharges into a zone of lower
velocity only if the 3 independent velocities (𝑦1,𝑦2, πΉπ‘Ÿ1) of the hydraulic jump equation confirm
the following equation. The relationship between the downstream and upstream depths is given by the following equation:

Hydraulic Jump equation
Hydraulic Jump equation

Where
y1 = Pre Jump depth of water (m)
y2 = Post Jump depth of water (m)
Fr1 = Upstream Froude number

In addition, the energy loss is given by the following equation:

Energy loss in hydraulic jump

where,
E1 = upstream energy, (m)
E2 = downstream energy, (m)
βˆ†E = energy loss, (m)

The head loss (hL), can be obtained from Munson Book:

head loss in hydraulic jump
Head loss in hydraulic jump
Demonstration of Hydraulic Jump

Objectives of the experiment:


a) To create the hydraulic jump.
b) To identify the different fluid flow types (subcritical flow and supercritical flow)
c) To compare measured flow depths with theoretical results.
d) To determine the energy losses and power losses through hydraulic jump.

Procedure:

  1. I started the pump to supply water to the flume.
  2. Then I placed the broad crested weir and adjust the sluice gate to develop hydraulic jump.
  3. I adjusted the position of the hydraulic jump by adjusting the amount of closure of sluice gate.
  4. I measured the depth of the bed of flume by using scale.
  5. In the next step, I measured water surface level before it had crossed the broad crested weir.
  6. Then I measured the weir head and weir height.
  7. Then I measured y1 & y2.

Results:

The calculation for Frequency 18 
Q (m3/sec)Y1 (m)Y2 (m)Y2/Y1V1 (m/sec)V2 (m/sec)Fr1Fr2E2 – E1 (m)HL (m)Remarks 
0.004820.0120.0252.0830.668750.32120.6490.001830.004558Weak Jump 
The calculation for Frequency 22
Q (m3/sec)Y1 (m)Y2 (m)Y2/Y1V1 (m/sec)V2 (m/sec)Fr 1Fr2E2 – E1 (m)HL (m)Remarks 
0.006490.0150.0352.33330.7210.3091.90.5280.003810.00165Weak Jump 
Classification of hydraulic jump
Classification of hydraulic jump

ERRORS:

  • The errors that may be possible to take place are under:
    Personal Errors:
  • Reading error due to water meniscus effect.
  • Parallax error (error due difference in the apparent position of an object viewed along
    two different lines of sight).
    Instrumental Errors:
  • Leakage of water may possible.
  • Sluice gate was on lateral slope (not horizontal).


IMPROVEMENTS:

  • Dye can be used to make fluid more clear and that will help us while calculating 𝑦1 and
    𝑦2.
  • Slow motion video camera can be used to record the footage of subcritical and
    supercritical flow to calculate 𝑦1 and 𝑦2 accurately.


SAFETY AND PRECAUTIONS:

  • Fix the weir firmly and strip tape should be smoothly placed to avoid leakage.
  • The channel should be cleared and dried with towel.
  • Safety shoes should be worn to avoid slipping that may cause accident.
  • Water should not be contaminated with any chemicals that may cause odor in tanks.

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Conclusion and Recommendations:


Both the hydraulic jump are classified as weak jumps.
During the experiment, we verified that the Froude number for the supercritical region was greater than one and for the subcritical region was less than one which is consistent with general experience. Secondly, we observed that hydraulic jump only occurs when the Froude number is greater than one. In the supercritical region, we have very high dynamic head and dynamic head drops in the subcritical region because of the turbulent mixing.
To create the hydraulic jump the Fr1 must be greater than one.

We can use a sluice gate in between the channel instead of the weir.

References:

Munson, Bruce Roy, 1940-. (2013)

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