Leonardo da Vinci was the first one to report the visualization of turbulent flow in his
famous sketches from 1510.
He described the existence of whirlpools of water in his notes. He wrote, “Observe the motion
of the surface of the water, which resembles that of hair, which has two motions, of which one
is caused by the weight of the hair, the other by the direction of the curls; thus the water
has eddying motions, one part of which is due to the principal current, the other to random
and reverse motion.” This notion is a precursor to the Reynolds flow decomposition of velocity
into mean and fluctuating parts, which Osborne Reynolds suggested 400 years later. He also
noted, “The small eddies are almost numberless, and large things are rotated only by large
eddies and not by small ones and small things are turned by both small eddies and large.”
Nowadays, the “small eddies” and the “large things” refer to turbulence and large-scale
coherent eddies, respectively. Leonardo da Vinci utilized his sketches as a flow visualization
method, providing clear information of turbulence behaviors and their effects.Figure 1. Leonardo da Vinci’s Sketches: Whirlpools of the Water (left), Vortices Behind
Obstacles (right): Arrows Indicate Flow Directions