We can verify the existence of these laminar, transitional, and turbulent
flow regimes by injecting some dye streaks into the flow in a glass pipe, as
the British engineer Osborne Reynolds (1842–1912) did over a century ago.
We observe that the dye streak forms a straight and smooth line at low
velocities when the flow is laminar (we may see some blurring because of
molecular diffusion), has bursts of fluctuations in the transitional regime, and
zigzags rapidly and randomly when the flow becomes fully turbulent. These
zigzags and the dispersion of the dye are indicative of the fluctuations in the
main flow and the rapid mixing of fluid particles from adjacent layers