Instability and transition of a radial liquid-film flow

In this paper, the instability and transition of a radial liquid-film flow which is regarded as a kind of boundary layer is described. This:flow has been generated by a water discharge to the atmosphere from the thin cylindrical gap between a pipe end and a disk surface. The spatial linear stability of the flow, including the effect of the radial spreading of vortices, is investigated. The numerical results show that the effect of the radial spreading of vortices increases the instability of the flow. The frequency of the most amplifying disturbance at each radial position, which is estimated from the evolution of the disturbance of the fixed frequency as it moves downstream, is in good agreement with that detected through wall pressure measurement. The correlation between the amplification of the linear disturbance with the transition point obtained by flow observation shows that the transition to turbulence occurs when the total amplification of disturbance is about e(9).