Large-scale volumetric particle tracking using a single camera: analysis of the scalability and accuracy of glare-point particle tracking

Abstract

Recent advances in tracer, illumination, and camera technology, paired with new processing algorithms, have been pushing the limits of scale for three-dimensional flow measurements. The present study explores the state of the art and discusses the current progress toward full-scale, in situ flow measurements in very large measurement volumes of order \(10\,\mathrm {m^2}\) or larger. In particular, we focus on industrial and environmental applications, where the measurement time, the processing time, and overall system cost all have to be minimized. With the glare-point particle tracking (GPPT) approach, we present a cost and time-efficient volumetric measurement technique using a single-camera setup, air-filled soap bubbles (AFSBs), and natural illumination. The GPPT approach was tested and characterized in a pyramidal-shaped measurement volume (\(V=18\;\textrm{m}^3\)) in an outdoor, open-jet wind tunnel. Bubbles of uniform size were produced by a bubble-generator prototype and illuminated by the sun. The uniform bubble size enabled a depth estimate for each bubble based on the glare-point spacing in the images from a single camera, thereby removing the need for additional cameras and perspectives. The measurement accuracy of the GPPT is then assessed by: (a) characterizing the performance of the bubble-generator prototype; (b) analyzing bubble deformation and its effects; and (c) assessing the accuracy of the depth estimate based on glare-point spacing. Finally, the scalability of the approach is discussed and, based on the light-scattering behavior of large AFSBs, a discussion is made of how GPPT will enable three-dimensional flow characterization in very large measurement volumes (\(V=\mathcal {O}(100\,\textrm{m}^3)\)) in the near future.