Optimization and integration of image-based schlieren and background-oriented schlieren techniques for two- and three-dimensional analysis of indoor airflows

本文主要研究基于图像的纹影技术和面向背景的纹影技术的优化与集成。这两种技术都允许在透明介质中显示由密度差异引起的折射率梯度。这些技术可以实现二维和三维评估，可视化和量化气流。在这些应用中，困难在于定义室内气流的小密度梯度。在这个项目中使用了一个独特的尺寸和质量的纹影镜。由于借助纹影镜捕获的纹影图像只能提供三维流场的二维投影，因此采用面向背景的纹影技术。初步研究表明，它的灵敏度几乎等于纹影镜的灵敏度。利用2台或5台相机捕捉背景纹影系统的测量场，可以对流场进行三维重建和定量评价。以往的研究表明，不可能对纹影镜和背景定向纹影技术记录的时空非定常流动进行定性或定量的比较。因此，该项目的目的是通过放置垂直于纹影镜的层析背景取向纹影系统来合并两个光学系统。结合这些技术，可以验证和开发各种流体重建方法。通过同时捕获气流，可以全面研究与建筑环境和室内空气相关的问题。

This proposal focuses on the optimization and integration of image-based schlieren and background-oriented schlieren techniques. Both techniques allow the visualization of refractive index gradients caused by density differences in transparent media. These techniques can be implemented for two and three-dimensional evaluation, visualization, and quantification of airflow. In these applications, the difficulty lies in the small density gradients that define the indoor airflow. A schlieren mirror that is unique in its size and quality is used in this project. As the schlieren images captured with the help of the schlieren mirror can only provide a two-dimensional projection of the three-dimensional flow field, the background-oriented schlieren technique is to be used. Preliminary investigations show that its sensitivity is nearly equal to the sensitivity of the schlieren mirror. With the help of two or five cameras that capture the measurement field of the background-oriented schlieren system, the flow can be reconstructed three-dimensionally and evaluated quantitatively.Previous studies indicate that it is not possible to qualitatively or quantitatively compare the spatial and temporal unsteady flows that are recorded by the schlieren mirror and the background-oriented schlieren technique. Therefore, an aim of this project is to merge both optical systems by placing a tomographic background-oriented schlieren system perpendicular to the schlieren mirror. Combining these techniques yields a substantial potential for validating and developing various flow reconstruction methods. By capturing the airflow simultaneously, problems that are associated with the built environment and the indoor air can be comprehensively investigated.