Interface Curvature Measurement of Liquid Film Based on SLIF

Interface curvature is essential for characterizing the morphology of liquid film at a deeper level. However, few researches have been conducted to investigate the interface curvature feature. In this paper, a scanning laser-induced fluorescence (SLIF) measuring system is introduced to perform the 3-D measurement of liquid film, and the principle of laser scanning is illustrated. Subsequently, slice image processing, contour interpolation and the volume rendering methods are utilized sequentially to reconstruct the 3-D liquid film. Moreover, the point cloud extraction and the curved surface fitting are carried out to calculate the normal vector and the coefficients in fundamental forms I and II. Furthermore, the interface curvature of 3-D liquid film is measured. The axial distributions of the principal curvatures under the different circumferential locations are investigated, and the results show that the extreme bending of liquid film interface is different under the different positions. Then, the joint probability density of principal curvatures is analyzed. The distribution range of minimum curvature is linearly related to the maximum curvature and decreases with the increase of liquid flow rate. In addition, the frequency distribution characteristics of mean curvature and Gaussian curvature are discussed, and the correlation to the circumferential liquid film thickness is also analyzed to study the bending characteristics of liquid film interface. Finally, the joint probability density of mean curvature and Gaussian curvature under the different flow conditions is further investigated. The results display that the shape of most interface waves is similar to spherical cup-shaped, and the bending degree decreases as the liquid flow rate increases. These experimental results are helpful to investigate the 3-D interface morphology of liquid film more deeply.