Unsteady Two-Phase Flow Measurements in Surges and Dam Break Waves

Flood waves resulting from dam breaks and flash floods have been responsible for numerous losses. In the present study, sudden flood releases were investigated down a large stepped waterway initially dry. A new experimental technique was developed to obtain instantaneous void fractions, bubble count rates and velocities. Unsteady air-water flow properties were recorded with arrays of conductivity probes. The results showed a strong aeration of the surge leading edge. Instantaneous velocity measurements indicated an unsteady turbulent boundary layer region with a potential flow above. In the unsteady boundary layer, void fraction and velocity data suggested a ratio of bubble diffusivity to eddy viscosity of about unity. Practically, the study provides new information on free-surface aeration in surging waters in channels and on beach slopes.