Study On Reconstructed Methods Of Three-Dimensional Optical Volume Computerized Tomography

With the rapid development of aviation, aerospace and military techniques, methods for diagnosing complex flow fields such as exhaust plume and aerodynamic flow fields of supersonic wind tunnel and rocket engine are urgently needed. Optical Computerized Tomography (OCT) has been considered as a powerful diagnostic tool for flow fields because of its nonintrusive and instantaneous, which be applied to many fields, such as flow visualization and measurement of physical parameters. It is a combination of optical methods such as interferometry, moire tomography and CT. Traditional CT reconstruction methods, however, is based on2-D Radon transformation and split the object into several parallel slices. Each slice is independently reconstructed by2-D CT reconstruction methods. It is obviously that traditional optical tomography is a pseudo3-D reconstruction method. To obtain an accurate3-D reconstructed result, the Volume Optical Computerized Tomography (VOCT) based on3-D Radon transformation is adopted to get a real3-D whole-field reconstruction. Moreover, this method can maintain the relevance between slices of the reconstructed field. But up to now, the reconstruction methods of VOCT have not been studied systematically. Thus, emphasis of this dissertation is put on the3-D algorithms of VOCT for the complex flow fields. The main works are summarized as follows:1. By combining volume CT method with interferometry, a real3-D reconstruction method via interferometric volume computerized tomography is discussed, which could reconstruct the measured flow field as a whole. This real three-dimensional method is verified by reconstructed the3-D temperature distribution of an actual hot flow field based on Mach-Zehnder interferometer.2. In order to realize the volume moire tomography, double cross gratings are applied in the moire deflected system to gain the shearing phase distribution of the grid moire pattern in two mutually perpendicular directions simultaneously. Thus, the scalar diffraction theory is used for analyzing the imaging process of the volume moire tomography based on double cross gratings to achieve the explicit form of shearing phase.3. According to the3-D Radon transformation and the shearing phase distribution of the grid moire pattern, the volume moire reconstruction algorithm is given and verified by the simulation experiment. Finally, the3-D temperature distribution of a propane flame has been reconstructed by moire reconstruction algorithms.4. According to the analysis of grid Moire fringes of volume moire tomography, spatial phase-shifting relations exist between grid Moire patterns corresponding to different spectrum. On this basis, a new optical system of volume moire tomography is proposed, which could obtain four spatial phase-shifting moire patterns simultaneously. With analysis of this system via scalar diffraction theory, the spatial phase-shifting characteristics between grid moire patterns are carefully analyzed.