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Air Entrainment of Free-Surface Tunnel Flow

Author(s): Juerg Speerli

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Keywords: Ir Entrainment; Free-Surface Tunnel Flow; Air-Water Flow; Air SupplySystem

Abstract: High-speed flow in bottom outlet tunnels involve air-water mixture flow. The air flow results from the subpressure downstream from the gate. The air entrained by the high-speed flow is supplied by the air supply pipe and the tunnel portal. As demonstrated, there is a relation between the two air supply discharges, independent of the individual supply rate. The present project refers to spray flow and free surface mixture flow. The latter flow configuration is recommended to inhibit choking of the tunnel flow. Further, a design equation for the required air supply discharge across the supply pipe is presented that inhibits significant subpressures in the gate vicinity. The effects of energy head on the gate, relative tunnel width, degree of gate opening and head loss coefficients are particularly significant, whereas the effect of tunnel length is only moderate.


Year: 1999

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