Investigation of large-scale circulations in room air flows using three-dimensional particle tracking velocimetry

Large-scale circulations in room air flows have been investigated with three-dimensional particle tracking velocimetry (3D PTV). This technique has been refined for large scales, enabling us to determine flow patterns, trajectories, and velocity vectors within a large cylindrical enclosure used as a model room for thermal convection. This test enclosure is called Rayleigh-Bénard (RB) cell and addresses the limiting case of room air with very high internal loads. The flow patterns are only created by buoyancy forces. The 3D PTV system consists of four CMOS cameras, two flash lamps, and an image recording and data processing system. Helium-filled latex balloons were used as tracer particles. The spatial resolution and accuracy were investigated in a test cell with the dimensions of 4 × 3 × 4 m3 by means of a given trajectory of a small glass sphere. First applications of the developed 3D PTV system in the large RB cell with a diameter of 7.15 m and a height of 3.58 m showed different characteristic flow patterns of large-scale circulation outside the boundary layers. From the recorded and analyzed long-term particle trajectories further important data of room air flows like velocity time series, probability density functions (PDF) of the velocity, and acceleration fluctuations were calculated. The proposed technique has a wide range of potential applications for the three-dimensional and time-dependent analysis of indoor air flows.