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Water Can Jump!!!! Hydraulic Jump Phenomena

Water Can Jump!!!! Hydraulic Jump Phenomena. Bader Anshasi Matthew Costello Alejandra Europa Casanueva Robert Zeller. Introduction. Due to excess kinetic energy (Fr> 1 ) Results in "jump" to a higher fluid height Increase in Potential Energy Seen both in nature and industry

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Water Can Jump!!!! Hydraulic Jump Phenomena

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  1. Water Can Jump!!!!Hydraulic Jump Phenomena Bader Anshasi Matthew Costello Alejandra Europa Casanueva Robert Zeller

  2. Introduction • Due to excess kinetic energy (Fr>1) • Results in "jump" to a higher fluid height • Increase in Potential Energy • Seen both in nature and industry • Rapids, waterfalls • Dams, spillways • Primary function is to dissipate energy • Increased Turbulence • Reduce erosion • Reduce damage to structures

  3. Examples

  4. Hydraulic JumpTheory

  5. Jump Requirements • Occurs during “Rapidly Varied Flow” • When flow depth changes rapidly in the direction of flow within a short length • Flow changes from supercritical to subcritical condition

  6. Froude’s Number • “Rapidly Varied Flow” can be characterized by the Froude’s Number • Fr =1at critical flow • V = velocity, g = gravitational constant, y = depth • A hydraulic jump occurs because of Fr changes: • Fr1 >1and Fr2 <1

  7. Phenomena • Flow depth increases abruptly with the formation of eddy currents • Kinetic energy is converted to potential energy • Results in a change of height • When eddies downstream of the jump break up, the fluid entraps air • The fluid loses energy after a jump • Leading to many practical applications

  8. Types of Hydraulic Jumps

  9. No hydraulic Jump • Fr<1 • Theoretically this would be a negative hydraulic jump, i.e. the fluid depth will decrease • Only physically possible if some external force accelerates the fluid at that point

  10. Undular Jump • For (1 < Fr1<1.7) • Characterized by: • Slight undulation • Two conjugate depths are close • Transition is not abrupt – slightly ruffled water surface

  11. Weak Jump • For (1.7<Fr1<2.5) • Characterized by: • Eddies and rollers are formed on the surface • Energy loss is small • The ratio of final depth to initial depth is between 2.0 and 3.1

  12. Oscillating Jump • For (2.5 <Fr1<4.5) • Characterized by: • Jet oscillates from top to bottom – generating surface waves that persist beyond the end of the jump • Ratio final depth to initial depth is between 3.1 to 5.0 • To prevent destructive effects this type of jump should be avoided

  13. Stable Jump • For (4.5<Fr1<9) • Characterized by: • Position of jump fixed regardless of downstream conditions • Good dissipation of energy (favored type of jump) • Considerable rise in downstream water level • Ratio of final to initial depth is between 5.9 and 12.0

  14. Strong or Rough Jump • For (Fr1 > 9) • Characterized by: • Ratio of final to initial depth is over 12 and may exceed 20 • Ability of jump to dissipate energy is massive • Jump becomes increasingly rough • Fr1 should not be allowed to exceed 12

  15. Hydraulic Jump Applications

  16. Practical applications • Engineers design hydraulic jumps to reduce damage to structures and the streambed • Proper design can result in a 60-70% energy dissipation • Minimizes erosion and scouring due to high velocities • Dams, weirs and other hydraulic structures

  17. Other Practical Applications • Recover pressure head and to raise water levels downstream of a canal • Maintain a high water level for irrigation or other water-distribution purposes • Mix chemicals in water purification • Aerate water for city water supplies • Remove air pockets from water to prevent air locking in supply lines

  18. Recreational Applications • Traveling down rivers/rapids • Kayaking and canoeing: playboat/surf hydraulic jumps

  19. Conclusion • An ideal design for energy dissipation would result in a “Stable Jump” • Characterized by a 4.5<Fr1<9 • Position of jump is fixed • Provides the most effective energy dissipation • Protects the structures and streambed by reducing velocity • Energy dissipation ranges from 45-70%

  20. Demonstration • Representing a hydraulic jump in your sink: Shallow fluid • A smooth flow pattern forms where the water hits • Further away, a sudden hydraulic jump occurs • Specific characteristics of this jump: • Water flows radially and it continues to grow shallower • It slows down due to friction (decrease in Froude number) up to the point where the jump occurs • From supercritical to subcritical flow • Diameter of the jump decreases as water depth increases.

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