CONVECTIVE INSTABILITY BOUNDARY OF COUETTE-FLOW BETWEEN ROTATING POROUS CYLINDERS WITH AXIAL AND RADIAL FLOWS

The convective instability boundary of a circular Couette flow in the annular region bounded by two co- or counter-rotating coaxial cylinder s with angular velocities omega(1) and omega(2), respectively, is stud ied in the presence of an axial flow due to a constant axial pressure gradient and a radial flow through the permeable walls of the cylinder s. A linear stability analysis is carried out for positive and negativ e radial Reynolds numbers corresponding to outward and inward radial f lows, respectively. Axisymmetric and non-axisymmetric disturbances are considered. In the particular case of no axial flow, the Couette flow is stabilized by an inward, or a strong outward, radial flow, but des tabilized by a weak outward radial flow. Non-axisymmetric disturbances lead to instability for some negative values of mu = omega(2)/omega(1 ). Bifurcation diagrams for combined radial and axial flows are more c omplicated. For particular values of the parameters of the problem, th e Couette flow has regions of stabilization and destabilization in the parameter space. Computational results are compared with experimental data. (C) 1997 American Institute of Physics.