AIR ENTRAINMENT OF FREE-SURFACE TUNNEL FLOW

摘要

High-speed flow in bottom outlet tunnels involve air-water mixture flow. The air flowrnresults from the subpressure downstream from the gate. The air entrained by thernhigh-speed flow is supplied by the air supply pipe and the tunnel portal. Asrndemonstrated, there is a relation between the two air supply discharges, independentrnof the individual supply rate. The present project refers to spray flow and free surfacernmixture flow. The latter flow configuration is recommended to inhibit choking of therntunnel flow. Further, a design equation for the required air supply discharge acrossrnthe supply pipe is presented that inhibits significant subpressures in the gate vicinity.rnThe effects of energy head on the gate, relative tunnel width, degree of gate openingrnand head loss coefficients are particularly significant, whereas the effect of tunnelrnlength is only moderate.