Transition phenomena in a spherical Couette flow between independently rotating spheres

The quasistatic laminar-turbulent transition of spherical Couette flow between two independently rotating concentric spheres for a gap ratio (ratio of the gap between two spheres to the inner-sphere radius) of 0.14 for which the Taylor instability occurs in the case of the inner sphere rotating and the outer sphere fixed has been investigated by simultaneous spectral and flow-visualization measurements. Rotation frequencies (phase velocities), scaled by the mean rotation frequency of both spheres, of various periodic disturbances do not depend much on the ratio $Ro*∕Ri*$ of the outer-sphere rotating Reynolds number $Ro*$ to the inner-sphere rotating Reynolds number $Ri*$⁠, although the phase velocity differs by the kind of disturbance. As disturbances unobserved in the case of the fixed outer sphere, traveling azimuthal waves only on an inflow boundary of toroidal Taylor-Görtler (TG) vortices and herringbone waves are observed in the case of co-rotating spheres, and spiral vortices and twists in toroidal TG vortices are observed in the case of counter-rotating spheres. Kinds and occurrence regions of flow regimes in the $Ro*-Ri*$ plane considerably differ by the history of $Ro*$ and $Ri*$⁠.