Note on the hydrodynamic eigenmodes of Couette flow

The axisymmetric eigenmodes for the velocity and pressure disturbances in the incompressible Couette flow between two concentric rotating cylinders with no-slip boundary conditions are computed numerically and plotted. As found previously in the narrow-gap approximation as well as for the Rayleigh-Bénard system, damped propagating viscous modes are present for wide ranges of parameters. Closed-form solutions for the special case of corotating cylinders show that the time constants for the decay of the eigenmodes then become insensitive to the ratio of the radii of the cylinders.