We extend upon the known flow transitions in neutrally buoyant particle-laden Taylor-Couette flows by accessing higher suspension Reynolds numbers in a geometry with radius ratio and aspect ratio. Flow transitions for several particle volume fractions () are investigated by means of flow visualization experiments, in a flow driven by a rotating inner cylinder. Despite higher effective ramp rates, we observe non-axisymmetric patterns, such as spirals, in the presence of particles. A novel observation in our experiments is the azimuthally localized wavy vortex flow, characterized by waviness present on a fraction of the otherwise axisymmetric Taylor vortices. The existence of this flow state suggests that in addition to the already established, destabilizing effect of particles, they may also inhibit the growth of instabilities. Flow topologies corresponding to higher-order transitions in particle-laden suspensions appear to be qualitatively similar to those observed in single-phase flows. A key difference, however, is the visible reduction in the appearance of a second, incommensurate frequency at higher particle loadings, which could have implications for the onset of chaos. Simultaneous torque measurements allow us to estimate an empirical scaling law between the Nusselt number (), the Taylor number () and the relative viscosity (. The scaling exponent of is non-trivially independent of the particle loading. Apparently, particles do not trigger a qualitative change in the nature of angular momentum transfer between the cylinders.

Ultrasound Imaging Velocimetry (UIV) is applied to a Taylor-Couette flow, for the case of pure inner cylinder rotation. By imaging a radial-azimuthal plane, two velocity components are obtained simultaneously in a two-dimensional plane. For the single-phase flow studies, Iriodin flakes (commonly used for visualizing flow structures) are used as “flow tracers” for the backscatter of ultrasound. This allows for a simultaneous mapping of the flow regime, via flow visualization, as well as extracting quantitative velocity information in the radial gap. After validating UIV against the analytically well-defined laminar Circular Couette flow as well as turbulent Taylor-Couette flow, other regimes are probed as well, in particular, the Wavy Vortex flow. Finally, the application of UIV to a particle-laden Taylor-Couette flow (particle volume fraction, f_0:01) is considered, under the conditions of oscillatory pure inner cylinder rotation. The results presented here serve as a proof-of-concept for the application of UIV to the Taylor-Couette flow and will be applied to denser particle-laden flows (f _ 0:05) in the future.