Hydraulic Model Study of Air Entrainment in Chute Spillways

Abstract

The objective of this study is to examine air entrainment in chute spillways that need for protectionfrom cavitation damage of spillway chute floors due to relatively high water velocity. The physical model was builtwith a scale 1:50 (model:prototype) for testing efficiency of air entrainment. The tested ratio of aerator stepheight with flow depth in spillway chute are varied as 1.5, 1.3, 1.0 and 0.6. Two air-shafts were installed at outsideof both chute walls beside the aerator step of the spillway of 25 m. crest length, equal to the width of chutehaving 30 degree floor slope. The experiment in this study was proceeded totally 110 cases including the test onchute floor with and without aeration devices. The experimental results showed that at velocities greater than 29m/s, the chutes need to install aeration devices for protecting chute floor from cavitation. The appropriaterecommended ratio of aerator step height with flow depth of water in chute (t/h) is 0.6. The studies resultsobtained relationship between the ratio of qa/q (air discharge per unit flow discharge) and the ratio of L/h(water jet length per flow depth of water), the relationship of jet jumping distance with velocity head, for rampwith 8 degree angle slope to the chute floor, and the relationship between the ratio of qa/q (air discharge perunit flow discharge) and the ratio of Aa/Aw (bothside air shaft area per water flow area at aerator upstream).These relationships from the study can be used as a guide for further design of air entrainment required in thechute spillways having 30 degree angle slope.