Abstract
Three-dimensional deformation and merging of disturbance waves in a radial liquid sheet was clarified. The radial liquid sheet is generated when flowing liquid film on a disk emerges radially from the disk edge. The radial liquid sheet is unstable because of a velocity profile with an inflection point (inflectional instability). The growth and deformation of the two-dimensional disturbance waves (D waves), which is formed by the instability, lead to laminar-turbulent transition just outside of the disk edge. In this study, the deformation process of the D waves was observed in detail with a CCD camera providing high temporal and spatial resolution images. Comparing the observed deformation of the D waves with the typical deformation of vortices formed by inflectional instability in a single-phase free shear flow, the three-dimensional deformations of the D waves and vortices were very similar. This suggests that three-dimensional deformation of the D waves is caused by enhancement of perturbed vortex filament in a braid region. However, merging of the D waves hardly occurred even though vortices in the free shear flow merge frequently. This implies that the existence of liquid surface prevents the merging of the D waves.
