Stilling basin
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This document discusses types of hydraulic jumps that can occur when upstream flow is supercritical, and describes how stilling basins are used to initiate jumps to dissipate energy without downstream damage. It notes that the "steady jump" type is best for design when the Froude number is between 4.5 and 9.0. Stilling basins use structures like baffle blocks to stabilize the jump position and control the jump. The length and design of the stilling basin depends on factors like the jump length and surface profile which relate to the upstream Froude number and flow velocity.
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Stilling basin
- 1. Types of Hydraulic Jump For hydraulic jump to occur, upstream flow must be supercritical (F > 1) • Type of jump depends on value of F1
- 2. Types of Hydraulic Jump
- 3. Hydraulic jumps used downstream of gates & other structures to dissipate energy & avoid damage downstream Best for design: “Steady Jump” 4.5 < F < 9.0 Avoid “Oscillating Jump” 2.5 < F < 4.5
- 4. Stilling Basins • Use stilling basin to initiate jump • Allows dissipation of energy within a structure that will minimize damage • Baffle blocks used to make jump position more stable
- 5. Stilling Basins: Design Considerations Length of jump Governs length of stilling basin Approximately 6 y2 for 4.5 < F1 < 13 Surface profile of jump – Governs height of sidewalls of – Dictates pressure on floor of basin – Depends on y1 and F1 • Control of jump (1) Chute Blocks (2) Baffle Blocks (3) End Sill Components used to initiate jump, stabilize jump, & make basin as short as possible
- 6. Control of jump by baffle piers
- 7. Control of jump by baffle piers
- 8. Stilling Basin Design • General stilling basin designs from USBR– Types I II III and IV based on F1 • Type I: 1.7 < F1 < 2.5 Weak jump No special structures needed 4 . 5 < F < 9 for best design Type II or III stilling basin Type II 4.5 < F1
- 9. TYPE III 4.5 < F1 Use for incoming velocity V1 < 60 ft/s
- 10. Use for incoming velocity V1 > 60 ft/s Dentated sill, no baffle blocks TYPE II 4.5 < F1
- 11. • Type IV 2.5 < F1 < 4.5 • Oscillating Jump, unstable • No baffle blocks because of wave action