Evaluation of bubble-induced turbulence using direct numerical simulation

The presented research evaluates the interaction between a single bubble and homogeneous turbulent flow using direct numerical simulation (DNS) approach. The homogeneous single-phase turbulence is numerically generated by passing a uniform flow through grid planes. The rate of the turbulence decay is validated against an experiment-based correlation. The single phase turbulence is then used as an inflow boundary condition for a set of single-bubble studies. We utilize a proportional-integral-derivative (PID) controller to ensure the statistically steady state bubble position and allow the detailed study of the turbulent field around the bubble. The effects of bubble deformability and the turbulent intensity on the quantity of bubble-induced turbulence are investigated separately. The existence of bubble creates new vortices in the wake region and the enhancement of turbulence is observed in the region behind the bubble. The results show that the magnitude of the turbulence enhancement would increase as the bubble encounters larger liquid turbulent intensity. Set of bubble Weber numbers from 0.34 to 2.71 are used to investigate the effect of bubble deformability. The more deformable bubble would increase the magnitude of turbulence enhancement behind the bubble. This research provides insight on the Bubble-Induced Turbulence (BIT) mechanism and is important for multiphase computational fluid dynamics (M-CFD) closure model development. (authors)