Abstract

Tiny and thin reflective flakes, such as aluminum powders, mica flakes or Kalliroscope, are widely used to visualize the flow structure in a closed container. From their brightness distribution we may obtain useful information on the flow, such as the occurrence of instability, the location of turbulent/non-turbulent boundaries, etc. However, it is not straightforward to identify which properties of the flow are reflected in the visualized patterns. We should note that it is not the orientation itself of the flake surface but its time-derivative that responds instantaneously to the velocity gradient. The orientation of flake surface has history effect and may not represent the local flow structure. In this talk we consider the mechanism of formation of brightness distribution of reflective flakes in flows in a precessing spherical cavity.