3D3C Velocity Measurement Around a Cubic Building Model in a Wind Tunnel Using a Single‐Camera Rainbow PTV Technique

ABSTRACT This study applies the rainbow particle tracking velocimetry (rainbow PTV) technique—a single‐camera method capable of three‐dimensional, three‐component (3D3C) velocity measurements—to airflow around a cubic block in a wind‐tunnel environment. Helium‐filled soap bubbles were used as tracer particles, and volumetric 3D3C velocity information was obtained over a measurement depth of 140 mm, with the cubic building model having a height of 100 mm. A dedicated processing pipeline, including color‐to‐depth mapping, particle tracking, and depth smoothing, was used to obtain particle trajectories and instantaneous vectors within the measurement volume. The technique successfully captured impingement, lateral divergence, upward motion over the block, and vortex shedding in the wake. Mean velocity fields were compared with reference hot‐wire anemometry measurements and showed good agreement in both upstream and wake regions. These results demonstrate that rainbow PTV can provide reliable volumetric velocity measurements in air using a single camera, offering substantially higher spatial coverage than pointwise methods and enabling analysis of unsteady flow phenomena.