Numerical investigation of hot and cold bubbles rising in water

Abstract

A compressible air bubble rising in water with heat transfer is simulated. We use the coupled level set and volume of fluid method to track the interface. The solver is verified with a non-isothermal static 3D bubble. The volume change of the bubble and the pressure difference between the inside and outside of the static bubble agree well with the theoretical solutions. Hot and cold 3D air bubbles rising in water are simulated and different rising paths are observed. The mechanisms underlying the path instability are elucidated by analyzing the vortex dynamics and shape deformation. We observe the hairpin vortex with 2R mode behind the rising bubble during the zigzag motion. The oscillation frequencies of the lateral bubble motion, the vorticity accumulation on the bubble surface, the forces exerted on the bubble in X and Y directions are the same while the oscillation frequencies of the aspect ratio and forces exerted on the bubble in Z direction are twice of that of the lateral bubble motion. The temperature changes faster in the rear part of the bubble due to the intensive water motion in the bubble wake. The volume-averaged water velocity presents a linear increase with the bubble rise while the kinetic energy displays a quadratic increase.