High-resolution velocimetry technique based on the decaying streaks of phosphor particles

This Letter introduces a new, to the best of our knowledge, particle streak velocimetry technique based on decaying streaks formed by individual phosphor particles following pulsed excitation. Tin-doped phosphor particles are dispersed into flows and excited by a pulsed UV laser light sheet. Emission streaks are recorded as a result of particle motion during the persistence of luminescence (here ∼27µs). The two components of the flow velocity are derived from the streaks without directional ambiguity by applying to each streak a two-dimensional fit describing a linearly moving point source with a mono-exponential decaying emission. This technique can achieve high spatial resolution compared to particle image velocimetry (PIV), while also requiring much fewer computational resources than particle tracking velocimetry (PTV) at high seeding densities. The wavelength-shifted luminescence also allows rejection of reflected laser light. The approach was validated in a free jet against simultaneous PTV and PIV and then successfully applied to measure a canonical boundary layer flow.