Research Article Steady Flow of a Second-Grade Fluid in an Annulus with Porous Walls

An exact solution of an incompressible second-grade fluid for flow between two coaxial cylinders with porous walls is given. It is assumed that the inner cylinder is rotating with a constant angular velocity and the outer one is at rest. The solution is expressed in terms of the confluent hypergeo-metric functions and it is valid for all values of the cross-Reynolds number and the elastic number. The solutions for −2, ∞, and − ∞ values of the cross-Reynolds number are obtained and a compar-ison with those of the Newtonian fluid is given. Furthermore, the torque exerted by the fluid on the inner cylinder is calculated. It is shown that the moment coefficient depends on the cross-Reynolds number, the elastic number, and the ratio of the radii of the cylinders. The variation of the moment coefficient with these numbers is discussed. Copyright q 2008 M. E. Erdoğan and C. E. İmrak. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1