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

• Applicant: Professor Dr.-Ing. Conrad Völker
• Subject Area: Construction Material Sciences, Chemistry, Building Physics ; Image and Language Processing, Computer Graphics and Visualisation, Human Computer Interaction, Ubiquitous and Wearable Computing
• Term: from 2020 to 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 444059583

• Final Report Year: 2024

Final Report Abstract

When visualizing and measuring airflow, invasive methods (e.g. anemometry, smoke, Particle Image Velocimetry etc.) are mostly used. However, these sensors or particles especially affect indoor airflows that are defined by small gradients. Alternatively, the so called schlieren imaging techniques (in particular the optical schlieren imaging technique and the background-oriented schlieren technique, BOS) can be applied. Both methods visualize density gradients in fluids non-invasively and can generate quantitative data during post-processing. Within the scope of the project “Optimization and integration of image-based schlieren and backgroundoriented schlieren techniques for two- and three-dimensional analysis of indoor airflows”, both methods were optimized and applied at the Department of Building Physics at the Bauhaus-University Weimar to analyze indoor airflow. During the research project, the system requirements of both schlieren imaging techniques were defined to increase the sensitivity of the setups. The sensitivity was then optimized to 0.1 K (schlieren imaging techinque with schlieren mirror) and 0.3 K (BOS). Furthermore, various methods were developed and implemented to quantify the visualizations. When working with the schlieren mirror and BOS, three-dimensional density gradients are always displayed on a two-dimensional plane (integration along the line of sight). However, when using more cameras with BOS, the flow field can be captured multi-dimensional. As part of the research project, two setups were developed to stereoscopically (2,5-dimensional with two cameras) and tomographically (three-dimensional with eleven cameras) capture the flow under investigation. During the funding period, both schlieren techniques were used to visualize airflow in various scenarios based on natural as well as forced convection.

Link to the final report

https://doi.org/10.34657/17585

Publications

• Einsatz von Filtern zur Reduktion der Ausbreitung der Atemluft beim Spielen von Blasinstrumenten und beim Singen während der COVID-19 Pandemie. In: Musikphysiologie und Musikermedizin 27 (3), S. 97–102
  Becher, Lia; Mühlenberend, Andreas; Gena, Amayu Wakoya & Völker, Conrad
  
• Risikoeinschätzung zur Ausbreitung der Atemluft bei Blasinstrumenten und Sängern während der COVID-19 Pandemie
  Becher, Lia; Gena, Amayu Wakoya; Völker, Conrad; Richter, Bernhard & Spahn, Claudia
  
• Risikoeinschätzung zur Ausbreitung der Atemluft beim Spielen von Blasinstrumenten und beim Singen während der COVID-19 Pandemie. 1. Update
  Becher, Lia; Gena, Amayu Wakoya; Völker, Conrad; Richter, Bernhard & Spahn, Claudia
  
• The spread of breathing air from wind instruments and singers using schlieren techniques. Indoor Air, 31(6), 1798-1814.
  Becher, Lia; Gena, Amayu W.; Alsaad, Hayder; Richter, Bernhard; Spahn, Claudia & Voelker, Conrad
  
• Sensitivity analysis of a largescale schlieren imaging setup when measuring indoor airflow. In: Proceedings of BauSIM 2022. Weimar, 20. - 22. September
  Gena, Amayu Wakoya; Becher, Lia & Voelker, Conrad
  
• The Spread of Exhaled Air and Aerosols during Physical Exercise. Journal of Clinical Medicine, 12(4), 1300.
  Alsaad, Hayder; Schälte, Gereon; Schneeweiß, Mario; Becher, Lia; Pollack, Moritz; Gena, Amayu Wakoya; Schweiker, Marcel; Hartmann, Maria; Voelker, Conrad; Rossaint, Rolf & Irrgang, Matthias
  
• Application of the background-oriented schlieren technique to visualize indoor airflows
  Benetas, Lia; Hartmann, Maria & Voelker, Conrad
  
• Tomographisches Background-Oriented Schlieren (BOS) zur Visualisierung von Luftströmungen. In: Proceedings of Bauphysiktage. Weimar, 06. - 07. März
  Benetas, Lia; Alsaad, Hayder & Völker, Conrad