Sep

18

Constructal Flow, from Jim Sogi

September 18, 2026 |

My friend Vic often mentioned Adrian Bejan's idea of the Constructal Law. Constructal flow is central a unifying principle of nature systems that results in the maximum efficiency on the transfer of energy.

Vic said the most important thing is, "What is the right question to ask?" Revisiting Bejan's books led me to ask, do back currents facilitate forward flow? Initially one would think not. I foil surf, and foils (one assumes) are designed to go fast. But, there is more to it.

Back currents—often called eddies or counter-currents—frequently facilitate forward or downstream progress in nature, engineering, and navigation. Rather than just working against the primary flow, these reverse-moving loops conserve energy, create circulatory balance, and allow travelers or aquatic organisms to move efficiently.

In biology, drag is any resistance from the fluid that slows motion, and in water it can come from body shape, rough surfaces, and body parts sticking out at odd angles. Smooth skin, compact fins, and a narrow profile all help reduce that resistance.

It is not just about being fast. A fish that saves energy on every stroke can spend more energy on feeding, escaping predators, migrating, or reproducing. That tradeoff matters a lot in biology, because form affects function. Even small shape changes can affect how efficiently an animal moves through its environment.

In foil surfing there is more than speed. One must launch off the water surface at low speed, be able to turn, to glide; all tradeoffs to speed, but absolutely necessary.

What is the purpose of backflow in the markets? As a natural system, the markets should create the maximum efficient transfer of capital to production of the best product and ideas.

There is some math for some of these issues.

Oliver Joseph responds:

Very interesting perspective. Large rivers have a hydrodynamic phenomenon called boils. These are caused by water moving at different speeds due to friction. Friction from the banks of the river, the bends and potentially deep under the water's surface a submerged tree or rock. In situations where the energy can’t go anywhere else but up you get a river boil. I have paddled a fair amount in the Mississippi watershed and boils are an awesome force to behold. You have to know how to navigate them (hit them hard with all you have dead on or a parallel approach). In an ideal laboratory setting you can create what’s called laminar flow but rivers are far from the lab. It's difficult to understand turbulent flow without first having an understanding of laminar flow (The complexities involved make many things for all intents and purposes unknowable). Mr A. Grimes has a wonderful exercise in his book where he urges his readers to create a predictable price data flow to test how your tools will react under controlled situations.


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