Controlling Turbulence and Evolution: How Engineers Overcome Uncertainty

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)

*Other videos in this series*

*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

[smartereveryday]

(Crashes through door, stumbles into room). Did someone say LAMINAR FLOW?

[Snotkoglen]

Ah. The David Attenborough of the engineering world. Could listen to you for hours. 😊

[Rathmun]

Even in situations where full scientific understanding _IS_ something we have, reality is messy. Just because you fully understand a process doesn't mean it's _easy_ to control it. The machinery to do the job perfectly may be far too expensive to construct, maintain, or train operators to use. So instead we engineer something that's _good enough, _ because it's cheaper than perfection, and we don't actually need perfection.

[serkles]

I've been studying engineering for 2 years now and at no point was this distinction between engineering and science made.

Here I was, thinking of engineering as an application of the scientific method to real world problems. I am both frustrated with myself and amazed at how well these past two episodes have portrayed engineering in a new and much more interesting light.

[Chriss]

glad you found time to make more videos. each one of your episodes is a true joy to watch and learn from.

[lemontec]

Strikes me that a lot of what’s happening in the field of Machine Learning today is not science but engineering. As with the discovery of the formula for what makes turbulent flow, it might take decades more to understand the principles behind it.

[helloxyz]

Directed evolution has been used by humans to develop specific traits in plants, birds, animals etc since before recorded history. Arnold's application to enzymes may have won her a nobel prize, but the basic process has been understood by farmers, dog breeders and mate-seekers for years.

[gtoger]

I've always shied away from using the terms "audio engineer" or "computer engineer" to describe the jobs I do, but that's come from a misunderstanding of what an engineer is or what makes an engineer. This new series helps me better understand that I have been using the engineering principal all along and don't need to be a lab-coat wearing scientist to be an engineer. Looks like I've got a new book to buy. Thanks, Bill, and welcome back!

[rianmach]

I just took a class called “scientific computing”, which funnily enough focuses entirely on approximating solutions to real world problems. In the class we learned how to evaluate a bunch of equations like optimization problems (essentially solving for x when an equation is traditionally impossible), and things like approximating the solution to second and n-order systems of differential equations which model different real-life systems. Although the pure math hasn’t quite gotten where it’d need to be in order to do these things, we can approximate a solution to them with nearly perfect accuracy using computing techniques developed long before computers ever were, by mathematicians like Euler and Newton. Thanks for coming back Bill!

[jamesmcpherson]

Thank you for this. I work in an engineering department where our needs are outpacing our certainty. I have felt guilty pushing for us to catalog our rules of thumb instead of waiting for guidance or more data. I feel much better about it now.

[Redmenace]

Very clear speaker! Very talented, and thank you for the post/content.

[hagerty]

So glad you're back. I got your book on the R101 (both audio and paper) had have referred to it often as an example of using completely non-intuitive solutions for problems (like the use of bovine intestinal tissue to make hydrogen gas bags).

Another use of Reynolds number, is that it makes wind tunnel testing of scale models possible. The air flowing over a small model will act quite a bit differently than on a full size aircraft at the same speed, so aero-engineers make sure to test at the same Reynolds number (Rn) to take into account the differences in size, which usually means running the air past at higher speeds.

This only works up until the transonic region, though (Rn is different at supersonic speeds), so NASA devised a clever way of increasing Rn other than the speed of the airstream. At their Ames Research Center, they build a pressurized wind tunnel where the whole thing is pumped up to two atmospheres. To have access to the test subjects without venting the whole tunnel (which takes several days to pressurize), they built the world's largest ball valve with the test section being the hole in the center. When they want to access the test subject, they rotate the ball 90° so that the center faces outwards and the rest of the tunnel stays sealed.

[XadackaPhotography]

I'm so happy that you're back making videos again. Excited to watch more!

[leonponce]

I have a degree in electrical engineering and only now I understood engineering is not (just) an application of science. It could predate science. It's hard to get this when they say you need to go through 4 semesters of calculus before starting to study electronics, because otherwise you wouldn't be able to understand the equationing of a RC circuit...

[cliffmathew]

Fascinating as always. People like Frances Arnold should be household names by now, and our kids should grow up hearing their stories. And once again, thank you very very much for explaining these concepts.

[zachrywd]

Engineering is just brute forcing nature to my will regardless of how the science works. I'd never thought of the relationship between those two methods like that... Mind blown, thx Bill.

[GRTJEH]

Hi Bill, Glad you're back here, here !
Just a quick side note: 4 min 50 to 5 min 20 is correct, but very confusing, because we normally work with a fixed flow rate (m³/s) and not a fixed velocity (m/s). This means that normally, one increases the diameters to get back in laminar flow, because the increased diameter drops the velocity squared. Doubling the diameter, means dividing the velocity by 4, effectively halving the Reynolds number with a fixed flow rate.

[johnsolod]

I'm an immortal highlander who has been studying liquid flows since 530BC (Heraclitus stole the whole river thing from me) & doing flow rate calculus for about 250 years, and I learned more from this video than during my entire cursed existence.

[TheHexCube]

I ❤ your channel and presenting style! I noticed the slower pace here too, an improvement for me - easier to digest. Thank you sir.

[jerrysstories]

Dude, I've been a fan ever since you stepped into the limelight with a a shiny aluminum can. I'm bummed whenever you don't post for a few years, and I'm happy to see you back. I sure wish you'd just become a full time YouTuber.