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A novel method for three-dimensional particle tracking velocimetry (PTV) is proposed that enables flow measurements in large volumes [ V = O(10 m 3 )] using a single camera. Flow is seeded with centimeter-sized soap bubbles, when combined with suitable illumination, produce multiple glare points. The spacing between the two brightest glare points for each bubble is then utilized to reconstruct its depth. While the use of large soap bubbles comes at the expense of non-Stokesian behaviour, the excellent ray optics allow for large volume illumination when coupled with for instance pulsed LED banks. Possible error sources and the out-of-plane accuracy are discussed before the feasibility of the method is tested in an industrial-scale wind tunnel facility (test section of cross section 9.1 m × 9.1 m). In particular, the vortical structure in the wake of a 30%-scale tractor-trailer model at a 9 • yaw angle is captured in a 4.0 m × 1.5 m × 1.5 m measurement volume. Long tracks of up to 80 time steps are extracted in three-dimensional space via a single perspective. The successful proof-of-concept confirms the potential of the novel approach for three-dimensional measurements in volumes of industrial scale.

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