| This Thesis examines the spatio-temporal response of Taylor-Couette flow and lid-driven vortex breakdown flow to time-periodic external forcing.; In Taylor-Couette flow, the outer cylinder is stationary while the inner cylinder simultaneously rotates and axially oscillates. We visualize a Neimark-Sacker bifurcation from a limit cycle to a torus. Alternating bands of frequency-locking and quasiperiodicity are observed and identified. Power spectra and Poincaré maps determine the rotation number variation across parameter space and detail the growth of resonance horns, which are not observed to interact in this study. The instability is observed as unsteady open spirals. Two modes, I and II, with azimuthal wavenumbers 1 and 2 are visualized. The flow topology exhibits strong axial and azimuthal periodicity. Beyond criticality, the cells destabilize rapidly into a spatially chaotic flow. Both modes occur without hysteresis, indicating a supercritical transition. The postcritical spatial structure is also investigated. The axial wavenumber variation is small, except in a localized region where very large gradients are found. This region correlates positively with the expected boundaries of the Neimark-Sacker bifurcation.; The normally steady vortex breakdown flow responds strongly to time-varying lid inclination. The one bubble state essentially precesses around the cavity axis. Only the bubble's downstream side is noticeably affected. The forcing causes fluid to be transferred from one side of the bubble to the other in a fairly periodic manner. Axial velocity contours in the meridional plane clearly illustrate the precessing nature of the bubble. Structure identified within the vorticity contours was strongly affected by the forcing. Without forcing, the contours show a large, well-defined, coherent structure, i.e. a bubble. With forcing, this coherent structure becomes very hard to distinguish, and it is unclear how the unsteady vorticity generated at the undulating endwall interacts with that present in the breakdown bubble. |
