A numerical study on flow and drag phenomena of spheroid bubbles in Newtonian and shear-thinning power-law fluids

Abstract

Effects of the Reynolds number, aspect ratio of spheroid bubbles, and power-law behavior index of shear-thinning liquids on the flow and drag behavior of spheroid bubbles are elucidated using a computational fluid dynamics-based numerical solver, ANSYS Fluent 14. The solution methodology is extensively benchmarked via detailed domain and grid independence study and by comparing present results of spherical bubbles in Newtonian and shear-thinning power-law fluids with their literature counterparts. Further extensive new results are reported over a wide range of pertinent conditions as follows: Reynolds number, Re: 1 – 200; aspect ratio of spheroid bubbles, e: 0.5 – 2.5, and power-law behavior index, n: 0.2 – 1. The size of the recirculation wake decreases with decreasing power-law index, and/or with decreasing bubble aspect ratio, and/or with decreasing Reynolds number. For bubbles of aspect ratio e > 1, a crossover Reynolds number is observed with respect to the power-law index, i.e. below the crossover Reynolds number, the drag coefficient of bubble increases with decreasing power-law index; whereas, above the crossover Reynolds number, a reverse trend is observed. Finally, based on the present numerical results, a simple predictive correlation is proposed for the total drag coefficients of spheroid bubbles rising in Newtonian and power law liquids, which can be used in new applications.