The First Visualization of Turbulent Flow

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