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We report results from the first systematic Lagrangian experimentalinvestigation in the regime of very light (air bubbles in water) and largeparticles (D/{\eta} >> 1) in turbulence. Using a traversing camera setup andparticle tracking, we study the Lagrangian acceleration statistics of ~3 mmdiameter (D) bubbles in a water tunnel with nearly homogeneous and isotropicturbulence generated by an active-grid. The Reynolds number (Re_{\lambda}) isvaried from 145 to 230, resulting in size ratios, D/{\eta} in the range of7.3--12.5, where {\eta} is the Kolmogorov length scale. The experiments revealthat gravity increases the acceleration variance and reduces the intermittencyof the PDF in the vertical direction. Once the gravity offset is subtracted,the variances of both the horizontal and vertical acceleration components areabout 5\pm2 times larger than the one measured in the same flow for fluidtracers. Moreover, for these light particles, the experimental acceleration PDFshows a substantial reduction in intermittency at growing size ratios, incontrast to neutrally buoyant or heavy particles. All these results are closelymatched by numerical simulations of finite-size bubbles with the Fax\'encorrections.

How gravity and size affect the acceleration statistics of bubbles in turbulence