放射状自由液膜流の不安定性に関する研究(流体工学,流体機械)

This paper describes the stability of a radial liquid sheet experimentally and theoretically. The liquid sheet was formed by the release of a radial liquid-film flowing on a disk from the edge of the disk to still air. When the Reynolds number is large, a concentric disturbance wave ('D wave') appears and grows downstream on both free surfaces of the liquid sheet. To clarify the root of 'D wave', its frequency was measured by a laser beam-reflection method and the cross-section of the wavy liquid sheet was observed by the LIF method. Temporal and spatial linear stabilities of the liquid sheet were also investigated. The frequency and wavelength of 'D wave' and the phase difference between 'D waves' on both liquid surfaces agreed well with those of the disturbance predicted by the stability theory. This means that 'D wave' on the liquid surface is caused by the unstable disturbance, which is attributable to the inflectional veocity distribution of the liquid sheet. It was also found that Gaster's simplified equation, which transforms the temporal growth rate to spatial one in the stability theory, is inadequate for a disturbance of large growth rate.