Bifurcation in narrow gap spherical Couette flow

Abstract

Incompressible Navier-Stokes equations in the spherical coordinates are solved using a pseudo-spectral method to simulate the problem of spherical Couette flow. The flow is investigated for a narrow gap ratio with only the inner sphere rotating. We find that the flow is sensitive to the initial conditions and have used various initial conditions to obtain di!erent branches of the bifurcation curve of the flow. We have identified three di!erent branches dominated respectively by axisymmetric flow, traveling wave instability, and equatorial instability. The axisymmetric branch shows unsteadiness at large Reynolds numbers. The traveling wave instability branch shows spiral instability and is prominent near poles. The traveling wave instability branch further exhibits a reversal in the propagation direction of the spiral instability as the Reynolds number is increased. This branch also exhibits a multi-mode equatorial instability at larger Reynolds numbers. The equatorial instability branch exhibits twin jet streams on either side of the equator, which becomes unstable at larger Reynolds numbers. The flow topology on the three branches are also investigated in their phase space and the found to exhibit a chaotic behavior at large Reynolds numbers on the traveling wave instability branch.