A Comparison of Flat White Aerosol and Rhodamine (R6G) Fluorescent Paints and Their Effect on the Results of Tomographic PIV Measurements

Methods for reducing surface reflections during PIV measurements are commonly discussed, but the effects of those surface reflections on PIV measurements are generally neglected. In this study, a comparison of light gathering characteristics of an experimental tomographic PIV system is made using a bluff body model that is coated: i) first, with a commercially available flat white aerosol paint and ii) second, with an airbrushed Rhodamine (R6G) fluorescent paint. For each coating, PIV measurements are compared from flow regions that are affected by either direct or indirect reflections. Measurements show that very little incident light is absorbed at white boundaries, producing strong light reflection; this effect, in turn: i) saturates the light signal from far-removed suspended particles and ii) greatly reduces the signal-to-noise ratio for particles situated even close to the receiving optics. By contrast, Rhodamine (R6G) fluorescent paint provides excellent surface reflection mitigation when paired with the 532 nm filters, producing a signal-to-noise ratio sufficient to allow uniform imaging of particles across the entire calibrated volume.