光学測定法を用いた水噴流自由界面波の統計的性質評価(<特集>第14回動力・エネルギー技術シンポジウム)

概要

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Free surface fluctuations at the neighboring two locations on a water jet have been evaluated using the developed non-intrusive optical technique. The free-surface slope angles are measured by detecting the two dimensional trajectories of laser beams refracted at the jet free surface. The obtained time series data of slope angles are divided into each wave period in accordance with the zero-up-crossing method. Then, the individual wave speed is evaluated from the dominant time lag of cross-correlation coefficient. The spatial shape of each wave is reconstructed by integrating the slope angle data. By comparing the analysis of wave shape statistics and the visual observation of free-surface photograph, it is found that the wave steepness reaches a maximum in the free surface region where a periodic wave train breaks down into less regular three dimensional patterns. In addition, the probability density functions of non-dimensional wave height are close to the Rayleigh distribution in the downstream region of wave breaking.
2010-03-25