Structure analysis of bubble driven flow by time-resolved PIV and POD techniques

In this paper, the recirculation flow motion and turbulence characteristics of liquid flow driven by air bubble stream in a rectangular water tank are studied. The time-resolved Particle Image Velocimetry (PIV) technique is adopted for the quantitative visualization and analysis. 532nm Diode CW laser is used for illumination and orange fluorescent (λ_ex = 540nm, λ_em = 584nm) particle images are acquired by a 1280×1024 high-speed camera. To obtain clean particle images, 545nm long pass optical filter and an image intensifier are employed and the flow rate of compressed air is 3ℓ/min at 0.5MPa. The recirculation and mixing flow field is further investigated by time-resolved Proper Orthogonal Decomposition (POD) analysis technique. It is observed that the large scale recirculation resulting from the interaction between rising bubble stream and side wall is the most dominant flow structure and there are small scale vortical structures moving along with the large scale recirculation flow. It is also verified that the sum of 20 modes of velocity field has about 67.4% of total turbulent energy.