FLOW OF NEWTONIAN AND NON-NEWTONIAN FLUIDS IN AN ECCENTRIC ANNULUS WITH ROTATION OF THE INNER CYLINDER

Three velocity components of a Newtonian and a weakly elastic shear-th inning non-Newtonian fluid have been measured in an annulus with an ec centricity of 0.5, a diameter ratio of 0.5, and an inner cylinder rota tion of 300 rpm. The results show that the rotation had similar effect s on the Newtonian and non-Newtonian fluids, with a more uniform axial flow across the annulus and the maximum tangential velocities in the narrowest gap in both cases. The secondary flow circulation with the N ewtonian fluid at a Reynolds number of 26,600 was in the direction of the rotation, with maximum values of 14% of the bulk velocity close to the inner pipe. With the 0.2% CMC polymer solution in laminar flow, r otation caused a narrow counter-rotating flow along the outer pipe wal l, which was absent at a Reynolds number 9200. The turbulence intensit ies in the region of widest gap were uninfluenced by rotation, increas ed in the Newtonian fluid, and decreased in the non-Newtonian fluid in the region of the smallest gap. The flow resistance of both fluids in creased with rotation at low Reynolds numbers and reduced with increas ing values to become similar to those of nonrotating flows. Comparison between rotating results of the Newtonian and non-Newtonian fluids at a Reynolds number 9200 and the same inner cylinder rotation, showed e ffects similar to those of nonrotating flow with extension of nonturbu lent flow, large reduction in turbulence intensities and drag reductio n of the order of 61% for the CMC solution. The swirl velocities in bo th fluids were similar when the Rossby numbers were similar. (C) 1997 by Elsevier Science Inc.