Topac, E. (2018). Design of a turbulent flow facility and development of an algorithm for PIV [Diploma Thesis, Technische Universität Wien]. reposiTUm. https://doi.org/10.34726/hss.2018.55264
The applications and investigations of anisotropic particles in turbulent flows are very extensive in plenty of industrial and natural processes. Anisotropic particles can vary in shape or rigidity and they exhibit rich and complex behaviours in turbulence, which are not completely understood. Therefore, dynamics of particle laden turbulent flows are extensively investigated. The aim of this work is to design a test section to detect anisotropic particles inside a turbulent channel flow. The channel has to be long enough to obtain a fully developed turbulent flow. The measurement technique to be performed should not be intrusive in order not to influence the flow field. Particle Image Velocimetry (PIV) is a non-intrusive laser optical measurement technique for research and diagnostics into flow, turbulence, microfluidics, spray atomization and combustion processes. Main components of a PIV system are: a test section, a high speed laser, a camera, and a computer to analyse the images obtained from the camera. In this work, optimization of the main tools of a PIV system will be vastly explained and the accuracy of the methods will be crosschecked by reviewing the literature. The optimization procedures substantially contain identification of the thickness of the walls of the optically transparent test section, lens and camera configurations and synchronization between cameras and laser. Different PIV techniques to obtain 3-velocity components will be introduced, a comparison and a discussion will be done in order to choose the most suitable method for our case by considering their advantages and disadvantages. The algorithm to analyse PIV data will be described step by step and the fundamental codes for programming a PIV analyzing algorithm will be given. The performance evaluation of the algorithm will be done by the comparison with direct numerical simulation results. During the comparison different subpixel accuracy methods were considered. Finally, a protocol containing the rules for lab safety, experimental setup, calibration and optimization was given.
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