THE NONAXISYMMETRIC INSTABILITY OF THE WIDE-GAP SPHERICAL COUETTE-FLOW

The nonaxisymmetric linear stability of spherical Couette flow is inve stigated numerically when the ratio of gap width to inner sphere radiu s (R(2) - R(1))/R(1) = 0.5. The basic flow becomes unstable at Re-c = 1245 and the associated azimuthal wave number is n(c) = 5, which agree s remarkably well with the experimental results by Egbers and Rath [Ac ta Mech. 81, 3 (1990)]. The marginal mode is oscillatory and has a dis tinctive wavy structure around the equator and spirals extended in eac h hemisphere. Sufficiently large spatial resolution is found to be req uired in order to avoid serious underestimation of the critical Reynol ds number. (C) 1997 American Institute of Physics.