A complete 3D particle tracking algorithm and its applications to the indoor airflow study

Abstract

While most research on particle tracking velocimetry (PTV) is devoted either to 2D flows or to small-scale 3D flows, this paper describes a complete 3D PTV algorithm and some applications to indoor airflow velocity measurements. A particle detection procedure especially adapted to the physical characteristics of neutrally buoyant helium-filled soap bubbles is described. To recover longer trajectories, a temporal tracking algorithm is used based on polynomial regression and including a cross-gap and a forward–backward strategy. In order to increase the measurement area and the number of trajectories, the correspondence problem is addressed by a new procedure involving fundamental matrices from both a three and a two-camera arrangement. 3D reconstruction is done by a least-squares method. Some guidelines are given in terms of camera and light positioning for 3D PTV in large volumes. Applications of the algorithm include Lagrangian tracking in (i) a 3.1 m × 3.1 m × 2.5 m light-gray walled test-room; (ii) a 5.5 m × 3.7 m × 2.4 m black walled test-room; (iii) over a heat source; (iv) inside an experimental aircraft cabin. Results show that the algorithm is capable of tracking more than 1400 tracers in volumes up to 3 m × 3 m × 1.2 m.