Stress Distribution around the Bubbles Rising Continuously along One Vertical Axis in a Viscoelastic Fluid

The stress distribution around the bubbles rising continuously along one vertical axis in a viscoelastic fluid was measured by transmitted light flow birefringence technique. A new method was developed for analyzing approximately an axisymmetric stress field. The method can be applied in the either case that the primary double refractive indices (primary stress differences) become larger toward the central axis or not. In order to evaluate quantitatively whether the method is effective for the analysis of the flow field around a single rigid sphere, the value of drag force acting on the sphere calculated from the measured stress distribution was compared with the directly measured value. The calculated values were about 20% larger than the measured values. By using this method, distributions of the primary normal stress difference and the shear stress r_rz could be obtained in the flow field around the bubbles rising along one vertical axis. Measurements were performed for three kinds of distance between the bubbles. Observed features of the distributions were consistent with the expected flow field. The quantitative evaluation of the method for the experimental result is still to be investigated especially in the region between the bubbles where the primary double refractive indices don’t become larger toward the central axis.