Controlling Turbulence and Evolution: How Engineers Overcome Uncertainty
Channel: engineerguy
Date: 2023-05-10

Two examples of how engineers solve problems _before_ they have scientific certainty: How they control whether or not fluid flow is smooth or turbulent, and how they engineer useful enzymes.

*Learn More: Companion Book*
Explore the ideas in this video series further with its companion book: _The Things We Make: The Unknown History of Invention from Cathedrals to Soda Cans_ (ISBN 978-1728215754)
https://www.amazon.com/Things-We-Make-Invention-Cathedrals/dp/1728215757

*Other videos in this series*
_Episode 1:_ Building a Cathedral without Science or Mathematics: The Engineering Method Explained https://youtu.be/_ivqWN4L3zU
_Episode 3:_ The Steam Turbine: The Surprising Relationship of Engineering & Science https://youtu.be/-8lXXg8dWHk
_Episode 4:_ The Microwave Oven Magnetron: What an Engineer Means by “Best” https://youtu.be/p8IO9u9IuOs

*Video Summary*

00:00 Titles

00:07 Laminar and Turbulent Flow
To illustrate how engineers work their way around uncertainty Bill introduces one of the most complex phenomena in nature yet one of utmost importance to engineers: the transition from laminar to turbulent flow. To illustrate these types of flow he examines the smoke rising from burning incense pointing out that the smoke near the incense flows smoothly (laminar flow) and further away becomes violently swirls (turbulent flow). 

00:51 Engineering & Turbulence 
He notes that to this day a fundamental understanding of when that transition from laminar to turbulent flow occurs puzzles scientists, yet, engineers must know when the transition occurs to control which type of flow occurs. Of prime importance is the smooth, laminar flow of air over an aircraft wing. Yet, without a fundamental scientific understanding of how to achieve that laminar flow we have flown across the Atlantic Ocean routinely since the first commercial passenger flights in 1939. 

1:23 Reynolds’s Apparatus
Although twenty-first century science cannot fully understand turbulence, a nineteenth-century engineering professor, Osborne Reynolds, built an apparatus to find a formula used by engineers to predict the transition from laminar to turbulent flow. Reynolds learned that a) below a particular flow rate no turbulence occurs, b) that the transition occurs abruptly, and c) that there is an upper limit to the flow rate above which smooth flow cannot be sustained.

3:10 Reynolds’s Explanation
To understand this behavior Reynolds compared the flow of water to a military troop. He reasoned that the orderliness of marching troops depends on three characteristics: speed, the number of soldiers in the troop, and discipline. The speed of the troop corresponds to the flow rate of the fluid, and the size of the troop to the diameter of the pipe. And the “discipline” is something called viscosity. It’s the resistance to flow. 

3:51 Viscosity: Water vs Honey
To understand viscosity, Bill compares the different rates of flow for water and honey: the water flows readily, while higher viscosity honey flows slowly. 

4:04 Reynolds’s Number
Reynolds gathered three characteristic of fluid flow — the diameter of the pipe, the velocity of the fluid’s flow, and its viscosity — into a single relationship: The diameter times the velocity divided by the viscosity. He observed that when this combination of variables was less than about 2,100 the flow was laminar and above that value the flow could became turbulent. 

5:16 Technological Importance of Flow
With this relationship engineers could know what to change to achieve laminar or turbulent flow. Bill mentions three designs where engineers want to control the type of flow: mixing pharmaceuticals, cooling steel, and directing the flow of air around a truck.

5:51 Science vs Engineering
Reynolds’s approach doesn’t describe turbulence at a molecular level, his description was phenomenological (that is, a description of what is observed). This difference underlines the striking difference between science and engineering: the scientific method strives to reveal truths about the universe, while the engineering method seeks solutions to real-world problems. 

6:10 Scientific Breakthroughs Only Change Boundaries
We might think that today’s science would subsumes all of engineering. Yet scientific breakthroughs never remove the need for engineering: Humankind developed the engineering method to reach beyond codified scientific knowledge. Instead, the advance of science only pushes out the boundary between the certain and uncertain, and so resets the boundary where engineers work. 

6:35 Directed Evolution
To illustrate that even today engineers step beyond scientific certainty, Bill tells the story of Nobel Laureate Frances Arnold’s evolution of enzymes that can be used under the harsh conditions of industrial use. 

12:01 Next Video
Bill mentions that in the next video he will explore the relationship of engineering to science. 

12:10 End Titles