Drag of a spherical bubble rising in power law fluids at intermediate reynolds numbers

The steady rise of a spherical bubble through an incompressible quiescent power law fluid has been studied numerically in the 2-D axisymmetric flow regime using the finite volume method. Based on the present numerical results, a predictive correlation in terms of Reynolds number (Re) and power law index (n) is proposed which enables the prediction of the total drag coefficient for the ranges of conditions as 5 <= Re <= 500 and 0.5 <= n <= 2 (hence covering both shear-thinning and shear-thickening type of fluid behavior). For n < 1, the drag is reduced below the corresponding Newtonian value, whereas it increases above its Newtonian value in shear-thickening fluids (n > 1). Thus, the drag coefficient increases with the increasing power law index for all values of the Reynolds number. The contribution of the pressure drag also increases with the increasing Reynolds number, though the shear-thickening behavior (n > 1) seems to suppress this tendency. In addition to the drag behavior, streamline and constant vorticity plots are presented to show the detailed nature of the flow and the effect of Reynolds number and power law index on the flow characteristics.