2001 Volume 34 Issue 7 Pages 912-918
This paper reports time-dependent flow characteristics of a turbulent water jet impinging vertically upward upon a water-air interface. Mexican-hat wavelet transform was applied to the time-dependent velocity fluctuations obtained in the region near to the air-water interface in order to analyze spatiotemporal turbulent structure at different time scales. The further understanding of the physical meanings of the wavelet transforms was tried by the analysis using logarithmic expectation and information entropy of information theory. It has been found that the near-interface turbulent structure is constituted not only by the impingement of the large-scale structure of the approaching turbulent jet but also by the time-dependent deformation of the surface bump. Time-series images of the surface bump visualized by an argon laser sheet technique showed some periodical regulation of the surface bump coming from the large-scale structure of the impinging jet.
