Experimental investigation on the turbulence channel flow laden with small bubbles by PIV

• The small bubble distribution was investigated by PIV.
• The small bubble modulation on the liquid turbulence was investigated by PIV.
• The influence of small bubbles on spanwise vortexes was studied with Lambda-2 vortex identification method.
• The small bubble modulation on the liquid turbulence was analyzed with POD.

Bubbly flows exist extensively in industrial fields, and thus it is important to understand deeply hydrodynamic characteristics of them. A turbulence channel flow laden with small dispersed bubbles was experimentally investigated by particle image velocimetry (PIV). Three phase discrimination methods between bubbles and tracer particles were introduced and compared in order to understand the turbulence modulation by small bubbles as accurately as possible. And Lamda-2 vortex identification and proper orthogonal decomposition (POD) methods were applied to analyze experimental results so as to deeply understand the influence of bubbles on the turbulence structure. The present experimental investigations show that most of bubbles accumulate near the wall, the violent accumulation of bubbles accelerates the liquid flow near the wall for the case with a relatively high void fraction, and it also reduces the liquid-phase turbulence intensity and Reynolds shear stress near the wall for the present two cases. POD analyses show that the bubble injection has an important influence on the large-scale structures of turbulence.