Flow Characteristics in Vertical Shaft Spillway with Varied Inlet Shapes and Submergence States

Abstract

A spillway is an essential hydraulic structure that discharges excessive water, especially during floods from upstream to downstream of the dam. A shaft spillway is sometimes used when a limited area is available. This study used four physical models of vertical shaft spillways with different edge shapes to study the flow characteristics. Each case was based on three tailwater heights: free, semi, and submerged. The results showed that two flow cases at the entrance depended on the water depth upstream; the weir flow happened at low discharge when the ratio of water depth to shaft diameter H/D was less than 0.5, and orifice flow when the proportion H/D was greater than 0.5. In the weir flow regime for submerged conditions, the water depth upstream (H) decreased by (6%) more than free flow. When replacing inlet shapes, the upstream depth (H) decreased by (40%) in the weir flow and (13%) in the orifice flow. In weir flow, the discharge coefficient values decreased with crest length, and larger values were obtained at the submerged state. While in orifice flow, Cd values increased with crest length, and higher values occurred at semi-submerged. Spillway discharge increased with entrance edge shape length in submerged condition.

Keywords

• Shaft spillway
• Flow regime
• Spillway
• Tail water
• Flow conditions
• Discharge coefficient