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"Temperature imaging in gas and liquid flows using luminescent particles"
The visualization and quantification of thermal mixing in turbulent fluid flows is key to the development of accurate turbulence modelling. These models are needed to predict the behaviour of flows in industrially relevant applications as well as geophysical flows (ocean, atmosphere, earth’s mantle, etc.). This talk will describe thermometry techniques based on luminescent tracer particles which can be combined with particle-based velocimetry to image both temperature and velocity in laboratory flows. The emphasis will be mostly on inorganic luminescent crystals, typically referred to as thermographic phosphors. These particles exhibit a wide range of luminescence properties and can be chosen to match the application needs, e.g., for use in cryogenic flows, at physiological temperatures, or up to 1000 K. There are also various implementations of this measurement concept. We can exploit the temperature dependence of the luminescence emission spectrum or the decay time of the particles to measure the temperature. The velocity can be measured simultaneously using temporally separated images of the particles using light scattering as in traditional PIV, using luminescence light or even single images of phosphorescence streaks caused by the motion of the particles during their luminescence decay. Recent developments include high-resolution measurements in submillimeter boundary layers, a proof-of-concept study of 3D temperature and velocity measurements in gas flows, and 2D thermometry in water with sub-°C precision. Finally, we will show how, through chemical synthesis, we can tune the particle luminescence properties to exactly match the temperature range of our application, for example, around 100°C to study boiling.
Bio:
Dr. Benoît Fond is in charge of luminescence-based optical diagnostics at ONERA, the French Aerospace Lab, and Paris Saclay University. After a French engineering degree and an MSc from the University of Florida, he obtained his PhD in Mechanical Engineering from Imperial College London in 2014. In 2016, he was appointed Junior Professor of Experimental Thermofluids at the University of Magdeburg in Germany and joined ONERA in 2021 to lead the development of pressure- and temperature-sensitive paints (PSP/TSP). Dr. Fond’s works focus on experimental fluid mechanics, leveraging luminescent materials for thermometry or pressure sensing, whether on surfaces or in fluid flows, with various applications for batteries, combustion, chemical processes, hydrogeology, aerodynamics, and more. Dr. Fond is also a lecturer at the international PSP/TSP course organized by DLR Göttingen, Germany, and was invited to the Laser Diagnostics for Energy and Combustion Science Gordon Research Conference in 2023.
