We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.
Technology

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

In Physics, what is a Boundary Layer?

By James Doehring
Updated: May 17, 2024
Views: 7,626
Share

A boundary layer occurs when a fluid flows past a fixed surface. It is typically defined as the region of fluid whose velocity is less than 99% of the unimpeded fluid flow. In other words, it is the zone of a moving fluid that is slowed down more than 1 percent by a stationary surface. The boundary layer has been defined to better understand fluid mechanics by dividing flow into two regions that display different behavior. Regions inside and outside of the boundary layer also generate friction in different ways.

An early problem in aerodynamics research was solving the complex Navier-Stokes equations, which are believed to govern the flow of fluid. There are many cases where the solutions to the Navier-Stokes equations are not known. It was noticed, however, that fluid flow exhibited two general modes of behavior: laminar and turbulent. Laminar flow is smooth and predictable flow, like that of a ball falling through honey. Turbulent flow is random and violent, like that coming out of a fire hose.

The boundary layer separates these two zones of fluid flow. Inside the boundary layer, the flow is primarily laminar. In this region, flow behavior is dominated by viscous stresses. Viscous stress is directly proportional to the velocity of a passing object; a highly viscous fluid, like honey, imposes much friction on objects moving quickly through it. Laminar flow is characterized by fluid flowing in parallel lines without irregularities.

Outside of the boundary layer, fluid flow is dominantly turbulent. Turbulent flow, whether in a liquid or gas, shows similar behavior. Chaotic variations in speed and direction of particles make precise predictions impossible with current knowledge. The effect of friction in turbulent flow is also different from laminar flow. Friction is generally no longer proportional to fluid velocity in the turbulent regimen.

The reason golf balls have dimples in them is related to the boundary layer of air. At low velocities, such as during putting, a perfectly spherical golf ball would not have much of a problem with air friction. During high-velocity flight, however, spherical golf balls would have a larger boundary layer than dimpled balls—which would mean more air is flowing by in the laminar way. This laminar flow would actually cause more air friction than a turbulent flow would. Dimpled golf balls fly further than their spherical counterparts because they have a smaller boundary layer and do not experience as much air friction.

Share
WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.

Editors' Picks

Discussion Comments
Share
https://www.wisegeek.net/in-physics-what-is-a-boundary-layer.htm
Copy this link
WiseGeek, in your inbox

Our latest articles, guides, and more, delivered daily.

WiseGeek, in your inbox

Our latest articles, guides, and more, delivered daily.