Study on multidirectional calibration of schlieren computerized tomography system

Schlieren technique is widely used in the visualization and measurement of combustion fields due to its high sensitivity. The data obtained by single-direction schlieren imaging is limited. With the improvement of measurement requirements, schlieren computerized tomography (CT) has become an important research direction. Schlieren CT reconstructs the test field from multidirectional projections. Due to inevitable system installation errors, the projections will be imaged at different positions on the sensors with different light intensities. In this paper, a parallel transmission schlieren CT system is designed with six directions. In order to solve the above problems, firstly, a multidirectional calibration method of schlieren CT based on affine projection is proposed to determine the internal and external parameters of the system. Then, the calibrated schlieren technique is used to establish the quantitative relationship between the grayscale values of the multidirectional schlieren images and the light displacements. With the calibration results, projections can be remapped to a unified coordinate system to reconstruct the three-dimensional distributions of the flow field.