Flow dynamics in the short asymmetric Taylor-Couette cavities at low Reynolds numbers

This paper reports on the numerical investigations of Taylor-Couette flow of radius ratio eta = 0.25-0.6 performed at low Reynolds numbers Re = 100-200. The inner cylinder and the bottom end-wall rotate, while the outer cylinder and the top end-wall are held fixed. A fully 3D DNS code based on the spectral Chebyshev - Fourier approximation is used. This study is complementary to those of Mullin and Blohm (Phys. of Fluids 2001, vol 13, 136-140) and Lopez et al. (J. Fluid Mech. 2004, vol 501, 327-354) where investigations have been performed for radius ratio 0.5. The 1-cell and 3-cell structures found by these authors are shown to exist for a wide range of radius ratios, and the transition processes between them are qualitatively similar. These structures show hysteresis, disappearing at saddle-node bifurcations which connect at a cusp point in the (Re, Gamma) plane. This cusp exists for the entire range of 0.1 < eta < 0.75, and it traces out a parabolic curve in the (Re, Gamma) plane, reaching a minimum Re at eta = 0.375. The detailed 3D DNS computations provide a lot of new information about such phenomena as the modulated rotating wave, the period doubling cascade and homoclinic collision. The results show that the period doubling bifurcation is important in the flow when the radius ratio is close to eta = 0.375.