Particle Image Velocimetry Using Novel, Non-Intrusive Particle Seeding

The purpose of this research effort was to study the use of non-intrusive particle seeding for Particle Image Velocimetry (PIV). Current seeding material and techniques involve the use of either solid particles or liquid mixtures which can contaminate or damage closed circuit wind tunnels, and in some cases can introduce a potential fire or explosive hazard. The proposed method is based on creating seed particles utilizing carbon dioxide (CO2). The CO2 would be dispensed into the flow as a liquid, immediately condensing to solid seed particles as they leave the spray nozzle. The advantage of using these particles is that they will sublimate from their solid state to harmless CO2 gas that would neither contaminate nor damage the tunnel and would not present a combustion hazard. The goal of this research is to determine if this technique is capable of yielding suitable CO2 seed particles, in an attempt to be able to ensure their suitability for Particle Image Velocimetry (PIV). Particle sizing data was acquired for a small-scale low-speed flow, and a size range on the order of 10 m was a common result for a variety of different nozzle and flow conditions. It was determined that with little modification, a commercial CO2 cleaning device created enough suitably sized seed tracer particles to execute PIV measurements and a proof-of-concept was successfully demonstrated in a supersonic flow using this technique.

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