Session

Session 4 2022

Start Date

10-26-2022 12:00 AM

Abstract

The United States Bureau of Reclamation (USBR) extensively studied hydraulic jump-type stilling basins for various inflow and tailwater conditions. They recommend Basin III using chute blocks, rectangular baffle blocks, and sloping end sill for medium to high dams. However, a significant contribution to the knowledge regarding the production of turbulence in discontinuity layers, the dissipation of energy, the convection, and the decay of turbulence in hydraulic jump was made by subsequent researchers. However, while developing the stilling basin, the wake formed by the jets separating at the front corners of the rectangular baffle blocks in Basin III and reattaching the downstream of the blocks was not considered. The use of Basin III was found limited to lower dams since cavitation of the baffle blocks was observed in many dams. After that, the use of wedge-shaped baffle blocks below a model spillway was systematically investigated. It was noticed that baffle blocks with a vertex angle of 1200 cut back at 900; the separating jets do not reattach downstream. Due to the wedge shape (super-cavitating), the low-pressure cavities do not collapse on the boundary. The new forms of baffle blocks are found to offer more drag to the flow when compared to rectangular blocks. Model tests were conducted to evolve stilling basins using the new baffle blocks and were highly successful. For example, in a stilling basin with an Inflow Froude Number of 7.07, with new blocks, a floor-length of about half the earlier suggested length is found to have better characteristics of scouring and sweep-out depth as compared to USBR Stilling Basin III.

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Oct 26th, 12:00 AM

Stilling Basins Using Wedge-Shaped Baffle Blocks

The United States Bureau of Reclamation (USBR) extensively studied hydraulic jump-type stilling basins for various inflow and tailwater conditions. They recommend Basin III using chute blocks, rectangular baffle blocks, and sloping end sill for medium to high dams. However, a significant contribution to the knowledge regarding the production of turbulence in discontinuity layers, the dissipation of energy, the convection, and the decay of turbulence in hydraulic jump was made by subsequent researchers. However, while developing the stilling basin, the wake formed by the jets separating at the front corners of the rectangular baffle blocks in Basin III and reattaching the downstream of the blocks was not considered. The use of Basin III was found limited to lower dams since cavitation of the baffle blocks was observed in many dams. After that, the use of wedge-shaped baffle blocks below a model spillway was systematically investigated. It was noticed that baffle blocks with a vertex angle of 1200 cut back at 900; the separating jets do not reattach downstream. Due to the wedge shape (super-cavitating), the low-pressure cavities do not collapse on the boundary. The new forms of baffle blocks are found to offer more drag to the flow when compared to rectangular blocks. Model tests were conducted to evolve stilling basins using the new baffle blocks and were highly successful. For example, in a stilling basin with an Inflow Froude Number of 7.07, with new blocks, a floor-length of about half the earlier suggested length is found to have better characteristics of scouring and sweep-out depth as compared to USBR Stilling Basin III.