The Effects of Wettability on Primary Vortex and Secondary Flow in Three-Dimensional Rotating Fluid**Supported by the National Natural Science Foundation of China under Grant Nos. 11862003, 81860635, 11462003, the Key Project of Guangxi Natural Science Foundation under Grant No. 2017GXNSF DA198038, Guangxi “Bagui Scholar” Teams for Innovation and Research Project

Abstract

The secondary flow driven by the primary vortex in a cylinder, generating the so called “tea leaf paradox”, is fundamental for understanding many natural phenomena, industrial applications and scientific researches. In this work, the effect of wettability on the primary vortex and secondary flow is investigated by the three-dimensional multiphase lattice Boltzmann method based on a chemical potential. We find that the surface wettability strongly affects the shape of the primary vortex. With the increase of the contact angle of the cylinder, the sectional plane of the primary vortex gradually changes from a steep valley into a saddle with two raised parts. Because the surface friction is reduced correspondingly, the core of the secondary vortex moves to the centerline of the cylinder and the vortex intensity also increases. The stirring force has stronger effects to enhance the secondary flow and push the vortex up than the surface wettability. Interestingly, a small secondary vortex is discovered near the three-phase contact line when the surface has a moderate wettability, owing to the interaction between the secondary flow and the curved gas/liquid interface.