Transition in a Free Liquid Film Flow Generated by a Rotating Disk

点击翻译按钮获取中文摘要

1. The transition from laminar to turbulent flow in a radial liquid film flow on a rotating disk is studied experimentally and theoretically. LDV measurements on the laminar flow clarified that a three-dimensional boundary layer grows gradually in the downstream direction and finally the entire flow merges into a three-dimensional boundary layer. High speed photography elucidated that the transition occurs owing to the amplification of the disturbance existing in the vicinity of the disk surface. The experimental results showed that the rotation of the disk suppresses the transition when the effect of the rotation of the disk on the flow is small, whereas the rotation promotes the transition when the effect is great. The linear stability of the flow was analyzed, where the effects of Coriolis force and streamline curvature were taken into account. The results showed that the instability of the flow changes, with an increase of the effect of the disk rotation on the flow, from a viscous- to an inflectional-type. It was also shown that the weak three-dimensionality of velocity profiles causes the decrease of the amplification factor of disturbance, suppressing the transition accordingly, whereas the strong three-dimensionality promotes the transition because of the inflectional instability.2. The effect of polymer additives on the transition of the liquid film flow on a stationary disk was studied experimentally and theoretically. Experimental results showed that polymer additives shift the point of the transition upstream and decrease the critical Reynolds number although the mechanism of the transition is the same as that of the solvent. The linear stability was studied for the liquid film flow of the dilute polymer solution. Calculated results showed that the elasticity of liquid given by the polymer additives increases the instability of the flow.