Flow mechanism of a submerged jet impinging on a free interface

This paper reports time-dependent now characteristics or a turbulent water jet impinging vertically upward upon a water-air interface. Mexican-hat wav elet transform was applied to the time-dependent velocity fluctuations obta ined in the region near to the air-water interface in order to analyze spat iotemporal turbulent structure at different time scales. The further unders tanding of the physical meanings of the wavelet transforms was tried by the analysis using logarithmic expectation and information entropy of informat ion theory. It has been found that the near-interface turbulent structure i s constituted not only by the impingement of the large-scale structure of t he approaching turbulent jet but also by the time-dependent deformation of the surface bump. Time-series images of the surface bump visualized by an a rgon laser sheet technique showed some periodical regulation of the surface bump coming from the large-scale structure of the impinging jet.