water can jump!!!! hydraulic jump phenomena
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Water Can Jump!!!!Hydraulic Jump Phenomena
Bader AnshasiMatthew Costello
Alejandra Europa CasanuevaRobert Zeller
IntroductionDue to excess kinetic energy (Fr>1)
Results in "jump" to a higher fluid heightIncrease in Potential EnergySeen both in nature and industry
Rapids, waterfallsDams, spillways
Primary function is to dissipate energyIncreased Turbulence
Reduce erosionReduce damage to structures
Examples
Hydraulic JumpTheory
Jump RequirementsOccurs 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
Froude’s Number“Rapidly Varied Flow” can be characterized
by the Froude’s NumberFr =1 at critical flow
V = velocity, g = gravitational constant, y = depth
A hydraulic jump occurs because of Fr changes:
Fr1 >1 and Fr2 <1
PhenomenaFlow depth increases abruptly with the
formation of eddy currentsKinetic energy is converted to potential energy
Results in a change of height When eddies downstream of the jump break
up, the fluid entraps airThe fluid loses energy after a jump
Leading to many practical applications
Types of Hydraulic Jumps
No hydraulic JumpFr<1
Theoretically this would be a negative hydraulic jump, i.e. the fluid depth will decreaseOnly physically possible if some external force
accelerates the fluid at that point
Undular JumpFor (1 < Fr1<1.7)Characterized by:
Slight undulation Two conjugate depths are close Transition is not abrupt – slightly ruffled water
surface
Weak JumpFor (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
Oscillating JumpFor (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
Stable JumpFor (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
Strong or Rough JumpFor (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
Hydraulic Jump Applications
Practical applicationsEngineers design hydraulic jumps to reduce
damage to structures and the streambedProper design can result in a 60-70% energy
dissipation Minimizes erosion and scouring due to high
velocitiesDams, weirs and other hydraulic structures
Other Practical ApplicationsRecover pressure head and to raise water
levels downstream of a canalMaintain a high water level for irrigation or
other water-distribution purposesMix chemicals in water purification Aerate water for city water supplies Remove air pockets from water to prevent air
locking in supply lines
Recreational ApplicationsTraveling down rivers/rapidsKayaking and canoeing: playboat/surf
hydraulic jumps
ConclusionAn 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%
DemonstrationRepresenting a hydraulic jump in your sink: Shallow
fluid A smooth flow pattern forms where the water hits Further away, a sudden hydraulic jump occursSpecific characteristics of this jump:
Water flows radially and it continues to grow shallowerIt slows down due to friction (decrease in Froude
number) up to the point where the jump occursFrom supercritical to subcritical flowDiameter of the jump decreases as water depth
increases.
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