2020-06-11

[public] 6.64M views, 241K likes, 2.95K dislikes audio only

Veritasium

Everyone loves laminar flow but turbulent flow is the real MVP.

A portion of this video was sponsored by Cottonelle. Purchase Cottonelle Flushable Wipes and try them for yourself: https://bit.ly/2WJm9Hq

Special thanks to:

Prof. Beverley McKeon and team https://www.mckeon.caltech.edu

Destin from Smarter Every Day https://www.youtube.com/smartereveryday

Nicole Sharp from FYFD https://ve42.co/fyfd

Pavol Dobryakov turbulent simulations: https://paveldogreat.github.io/WebGL-Fluid-Simulation/

I got into turbulent flow via chaos. The transition to turbulence sometimes involves a period doubling. Turbulence itself is chaotic motion, it is unpredictable and sensitively dependent on initial conditions. What surprised me is all the ways turbulent flow is useful to us. It is diffusive, meaning it causes mixing. This is useful in jet engines or rocket nozzles (which Destin studies) and is important to achieve in microfluidic devices, which are so small that turbulent flow is actually difficult to achieve. Turbulent flow can energize a boundary layer, which is important to maintain flow attachment over a wing, maintaining lift and delaying stall. Similarly a turbulent boundary layer over a golf ball reduces pressure drag allowing golf balls to fly further. This is the reason for the dimples on golf balls. Flow transitioning to turbulence in the wake of a bluff body can create periodic vortex shedding. This beautiful phenomenon can be seen in the von Kàrmàn vortex street in clouds viewed from space. Turbulence is everywhere, in the air currents in a room, in your aorta, in the breaths you exhale, in oil pipelines and water pipes, in the flow over cars and ships and planes. Animals have evolved for it (like dead fish swimming up stream) and we have engineered our environment, our planes and golf balls for it. Laminar flow may be nice to look at (which is why we use it in decorative fountains) but turbulent flow does the real lifting.

Animations by:

Jonny Hyman (Sun, Jupiter, Reynolds, airfoil, Earth time-lapse)

Research and writing:

AJ Fillo and Derek Muller. AJ also created the wind tunnel golf ball shots

Filmed by:

Daniel Bydlowski and Derek Muller

Additional footage:

Images of Jupiter courtesy of NASA

Turbulence in air currents by the Physics Girl, Dan Walsh, and Grant Sanderson /youtube/video/N7d_RWyOv20

/youtube/video/_UoTTq651dE

Music:

illBird "Shaffuru" https://youtu.be/5rkt53fNMgc

From EpidemicSound https://epidemicsound.com "Seaweed" "Colorful Animation 4"

Kevin MacLeod https://incompetech.com "Sneaky Adventure"