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

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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.