Tomographic background-oriented schlieren (BOS) is used to measure three-dimensional instantaneous density fields in turbulent flows. Density gradients are related to the refractive index through the Gladstone-Dale relation. Based on path-integrated apparent displacements in a background pattern from path variations in light rays travelling through the flow, a tomographic reconstruction of the three-dimensional refractive index gradients can be obtained. A Poisson equation of the reconstructed gradients is solved to obtain the refractive index field. We examine four sources of measurement error: (i) defocus blurring; (ii) spatial averaging in the finite difference scheme for solving the Poisson equation; (iii) limited-view tomographic reconstruction; and (iv) displacement field noise. Synthetic BOS displacements are generated from the instantaneous density fields of a heated jet at a Reynolds number of 10 000 and jet exit centreline-to-ambient density ratio of 0.83 computed via ...

中文翻译：

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从断层扫描背景下的有色裂痕（BOS）评估三维密度测量

面向背景的断层扫描谢里伦（BOS）用于测量湍流中的三维瞬时密度场。密度梯度通过Gladstone-Dale关系与折射率相关。基于背景图案中的路径积分视在位移（由于流经该光线的光线的路径变化而引起的位移），可以获得三维折射率梯度的层析成像重建。求解重构梯度的泊松方程以获得折射率场。我们检查了四个测量误差源：（i）散焦模糊；（ii）求解差分泊松方程的有限差分方案中的空间平均；（iii）有限视野断层扫描重建；（iv）位移场噪声。