Water Can Jump Hydraulic Jump Phenomena Bader Anshasi

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 �Rapids, waterfalls �Dams, spillways �Primary function is to dissipate energy �Increased Turbulence �Reduce erosion �Reduce damage to structures

Examples

Hydraulic Jump Theory

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

Froude’s Number �

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

Types of Hydraulic Jumps

No hydraulic Jump �

Undular Jump �For (1 < Fr 1<1. 7) �Characterized by: �Slight undulation �Two conjugate depths are close �Transition is not abrupt – slightly ruffled water surface

Weak Jump �For (1. 7<Fr 1<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 Jump �For (2. 5 <Fr 1<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 Jump �For (4. 5<Fr 1<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 Jump �For (Fr 1 > 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 �Fr 1 should not be allowed to exceed 12

Hydraulic Jump Applications

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

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

Recreational Applications �Traveling down rivers/rapids �Kayaking and canoeing: playboat/surf hydraulic jumps

Conclusion �An ideal design for energy dissipation would result in a “Stable Jump” �Characterized by a 4. 5<Fr 1<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%

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.