Void fraction estimation using a simple combined wave gauge system under breaking waves

Abstract

In this study, a unique experimental technique that is capable of quantifying void fraction under two-phase airwater flows based on simple combined resistance and capacitance wave gauge system is described and the subsequent applications are discussed. The technique is validated under various surf-zone breaking waves of different wave periods and wave heights in the 2-dimensional wave flume. The difference in the measured surface elevations by capacitance and resistance wave gauges is positively linked to the depth of aeration and depth-averaged void fraction, that is validated by the corresponding images. The measured depth-averaged void fraction at the passage of the air cavity formed by the overturning jet after breaking showed a distinct pattern in regular and cnoidal waves which is attributed to different amount of droplets generated during the jet-curling process. Based on wavelet analysis, the peak frequency-wave continuously spreads its energy to its superharmonic components due to shoaling while instantaneous spreads of wave energy to the higher harmonics are superposed due to breaking and subsequent jet-overturning. Considering void fraction, a sharper decay of wave energy within the intensely aerated region immediately after breaking is observed and the dissipated energy is reduced as the wave steepness increases following an exponential decay.