Air concentration measurements in highly-turbulent flow on a steeply-sloping chute

Abstract

The U.S. Bureau of Reclamation's (Reclamation) stepped spillway overtopping protection research program required air concentration profile data be obtained during testing in a large, 15.2-m-high outdoor flume. The air concentration profiles were needed with velocity profiles to evaluate energy dissipation, bulking, and model/prototype correlation with a smaller indoor model. A probe was developed to measure air concentration in a free-surface, highly-aerated flow. The probe acts as an air bubble detector and is based upon the difference in electrical resistivity between air and water. The basic components of the air bubble detector and its operation are discussed. A sample of the measured air concentration profiles is given with basic comparisons made to published data on aerated flow. The success of the measurements with this instrument means its use could improve the ability to measure the volume of air in an air/water mixture, for a known water flow, in numerous situations.