Three-Dimensionality of Trajectories of Experimental Tracers in a Steady Axisymmetric Swirling Flow: Effect of Density Mismatch∗

The motion of tracer particles used for visualization in a steady axisymmetric swirling flow in a closed rotating disk–cylinder system is studied numerically. It is assumed that there exists a density mismatch between the particles and the fluid. It is shown that such a slight density mismatch leads to a deviation of the particle motion from steady axisymmetric streamlines, which in its turn yields nonaxisymmetric patterns of the visualized flow. This gives a possible explanation for an existing disagreement between several experimental and numerical studies.