Fluorescent Particle Flow Imaging

Abstract: Recent progress in interpreting and using fluorescence signals emitted from flow seeding particles has led to innovative applications for flow imaging. While a number of approaches exist, our group at Virginia Tech has shown advances using particles doped with a safe dye, Kiton Red 620, specially devised for aerodynamics applications wherein users may inhale low concentrations of particles during normal working practices. In a collaboration with researchers at NASA Langley Research Center, polystyrene spheres were synthesized to contain optimal concentrations of this dye, while holding a stringent tolerance around a nominal diameter of 0.87 μm. The resulting particles have been shown to work in aerodynamics studies as tracers for both fluorescent laser Doppler velocimetry and fluorescent particle image velocimetry. By using the fluorescence signals, dramatic improvements in laser scattering from surfaces and interfaces are realized, such as the comparison shown in Figure 1 between fluorescent and conventional Mie-scattering PIV. This capability enables near-surface flow studies in complex devices, even without other advanced treatments or specialized facilities.

In the presentation, a brief review of the literature of fluorescent particle flow imaging will be provided. A basic description of the metrology implications will be described at a fundamental level. The specific particle technology developed by Virginia Tech and NASA will be placed in context with other technologies, and its basic performance for imaging applications presented. Aerodynamics applications using the Kiton Red 620-doped particles will be shown to offer dramatic improvements in near-surface particle imaging quality, without the need for special treatment of flow models. Some other advanced uses for the particles, such as flow temperature measurements, will be discussed. Finally, the outlook for advancing the state-of-the-art in fluorescent particle flow imaging will be proposed.

Figure 1. Images of (a) fluorescent particles and (b) Mie scattering from the same particles for flow imaging at an angle to a surface as in (c). This figure excerpted from: Petrosky, B.J., Lowe, K.T., Danehy, P.M., Wohl, C.J. and Tiemsin, P.I., 2015. Improvements in laser flare removal for particle image velocimetry using fluorescent dye-doped particles. Measurement Science and Technology, 26(11), p.115303.