Experimental and numerical investigation on the accuracy of phosphor particle streak velocimetry

A new phosphor particle streak velocimetry (phosphor-PSV) diagnostic with high spatial resolution was recently demonstrated (Fan et al. in Opt Lett 46:641, 2021), where individual phosphor particles, excited by a short pulse laser, form streaks as a results of their displacement by the flow during their relatively long luminescence decay. The local flow velocity is derived by fitting each phosphor streak as a two-dimensional linearly-moving point source with a mono-exponential decaying emission. This single-pulse, single-exposure technique yields a vector for each particle, as in particle tracking velocimetry, avoiding the spatial filtering associated with particle image velocimetry (PIV). The wavelength-shifted luminescence also allows rejection of unwanted reflected laser light, and macroscopic measurements in Fan et al. (Opt Lett 46:641, 2021) were obtained at a distance of 30 μ m from a wall. In this manuscript, we establish by a combination of experiments and luminescent particle imaging simulations the performance of the technique in a range of flow conditions and imaging parameters. A new image segmentation algorithm is developed and applied to phosphor streak images to improve the density of measurements to 0.004 vectors per pixel (vpp). Two phosphors with decay times of 564.2 μ s (Gd2O2S:Tb ) and 0.92 μ s (BaMgAl10O17:Eu ), are used to perform measurements in slow liquid flows (< 20 cm/s) and fast turbulent jets (up to 85 m/s), respectively. To assess the uncertainty of the approach for various experimental parameters (phosphor particles, flow velocity, particle image size, signal-to-noise ratio, and streamline curvature), synthetic streaks are generated and validated against experimental data. Finally, the impact of out-of-plane motion is investigated experimentally. This study paves the way for a wide implementation of the new phosphor-PSV technique in flow research and, in particular, to study two-phase flows and confined or semi-confined flows near solid boundaries.