3D Measurements of a Two-phase Flow inside an Optical Cylinder Based on Full-Field Cross-Interface Computed Tomography

Abstract

Three-dimensional (3D) tomographic reconstruction in confined-space requires a mapping relationship which considers the refraction distortion caused by optical walls. In this work, a tomography method, namely full-field cross-interface computed tomography (FCICT), is proposed to solve confine-space problems. The FCICT method utilizes Snell’s law and reverse ray-tracing to analytically correct imaging distortion and establishes the mapping relationship from 3D measurement domain to 2D images. Numerical phantom study is first employed to validate the FCICT method. Afterwards, the FCICT is applied on the experimental reconstruction of an illuminated two-phase jet flow which is initially generated inside an optical cylinder and then gradually moves outside. The comparison between accurately reconstructed vapor by FCICT and coarse result by traditional open space tomography algorithm provides a practical validation of FCICT. Based on the 3D vapor reconstructions at different time sequences, the distributions of surface velocity and 3D curvatures are calculated, and their correspondences are systematically analyzed. It is found that the velocity of a surface point is positively correlated with the mean curvature at the same point, which indicates the concavity/convexity of vapor surface is possibly in accordance with the surface velocity. Moreover, the surface velocity presents monotonical increasing trend with larger Gaussian curvature for elliptic surface points only, due to the dominated Brownian motion as the vapor develops.