Tag: turbulent flow

Studying Hydroelastic Turbulence
Can energy at the small-scales of a turbulent flow work its way up to larger scales? That’s a question at the heart of today’s study. Here, researchers are studying hydroelastic waves — created by stretching a thin elastic membrane over a water tank. The membrane gets vibrated up and down in just one location with an amplitude of about 1 millimeter. The resulting waves depend both on the movement of the water and the elasticity of the membrane, mimicking situations like ice-covered seas.
Rather than simply dying away, the local fluctuations introduced at the membrane spread, coalescing into larger-scale hydroelastic waves. How energy flows between these scales could have implications for weather forecasting, climate modeling, and other turbulent systems. (Image and research credit: M. Vernet and E. Falcon; via APS)
Fediverse Reactions
August 21, 2025
Using Turbulence in Flight
When small, heavy particles are in a turbulent flow, they settle faster than in a quiescent one. Their interactions with turbulent eddies sweep them along, extracting energy that lengthens their overall path but reduces the time necessary for them to fall. Using the same principles, researchers are finding ways for rotorcraft and other vehicles to extract energy from turbulence for more efficient flight.
The technique forces a vehicle to behave like a heavy particle by sensing turbulent gusts from its own accelerations and adding forcing to those accelerations when they are in the desired direction of flight. In essence, the vehicle uses the turbulence of its surroundings to find helpful tailwinds. (Image credit: A. Soggetti; research and submission credit: S. Bollt and G. Bewley)
May 12, 2022
Swapping Emulsions
Chemically speaking, oil and water don’t mix. But with a little fluid mechanical effort, it’s possible to make them an emulsion — a mixture of oil droplets in water or water droplets in oil. Researchers in the Netherlands discovered that the viscosity of these emulsions depends critically on which of those mixtures you have.
To create their emulsions, the team used a tank consisting of two concentric cylinders. When the inner cylinder spins, it creates a well-understood flow field between the inner and outer cylinder. By varying the ratio of oil to water in the tank, they could explore a wide range of emulsions. They found that the emulsion’s viscosity changed dramatically when the emulsion shifted from oil droplets in water to water droplets in oil, something known as a catastrophic phase inversion. During this switch the viscosity dropped from 3 times higher than pure water to 2 times lower! (Image credit: A_Different_Perspective; research credit: D. Bakhuis et al.; via APS Physics; submitted by Kam-Yung Soh)
April 13, 2021
Celebrating Turbulence
Laminar flow is easy to love, but turbulence is a far richer phenomenon. That’s the premise behind Veritasium’s new video (and, yes, I agree with him). In the video Derek provides a nice introduction to turbulence, including a checklist of qualities a turbulent flow must have.
Personally, I don’t classify flows as simply being either laminar or turbulent; I view those two states as ends of a spectrum, which means there are many flows that fall somewhere in-between. (For more on what happens between laminar and turbulent, check out my video on transition.)
As neat and eye-catching as laminar flow can be, turbulence is critical to life as we know it. It’s a necessary ingredient in cloud and raindrop formation. It drives the mixing of blood in our hearts. It keeps the leaves on trees from overheating. Without it, your coffee would be cold long before your cream mixes in. Turbulence is even critical to star formation; without turbulence, our entire solar system might have lacked the matter and time necessary to form! (Video and image credit: Veritasium)
June 19, 2020
New Signs of Turbulence in Blood Flow
Our bodies are filled with a network of blood vessels responsible for keeping our cells oxygenated and carrying away waste products. In many ways, our blood vessels are tiny pipes, but there’s a crucial difference in the flow they carry: it’s pulsatile. Because the flow is driven by our hearts, rather than a continuous pump, every heartbeat creates a distinct cycle of acceleration and deceleration in the flow. And new research has found that this cycle, when combined with curvature or flow restrictions like plaque build-up, can create turbulence in unexpected places.
Specifically, the researchers found that decelerating pipe flows can develop a helical instability that breaks down into turbulence, even in vessels where purely laminar flow would be expected. In the animations above, you can see the flow slow, develop swirls and then break into turbulence. The flow becomes laminar again as it accelerates, but during that brief bout of turbulence there’s much higher forces on the walls of a blood vessel. Over time, that extra force could contribute to inflammation or even hardening of the arteries. (Image and research credit: D. Xu et al.; via phys.org)
June 1, 2020
River Avon
One of the challenges in fluid dynamics is considering the instantaneous versus the average. Many flows — especially turbulent ones — are different at every point in space and in time. That’s a lot of data to collect and to wrap one’s head around. So often researchers will average turbulent measurements over a period of time and break that information down into two variables: an average velocity and a fluctuating one.
What does that have to do with this image? Well, by capturing the River Avon’s flow near Pulteney Bridge as a long exposure, photographer Peter Leadbetter gives us a look at the river’s “averaged” flow. The long exposure smooths out some of the intermittent features visible in a faster picture, and instead draws our attention to the overall path of the flow and regions that may behave differently, like those near the wall in the foreground. The averaging researchers do is much the same. It will erase or obscure some features while making the large-scale patterns more obvious. (Image credit: P. Leadbetter; submitted by Ioanna S.)
January 13, 2020
Order in Chaos
Although turbulent flow is chaotic, it’s not completely disordered. In fact, order can emerge from turbulence, though exactly how this happens has been a long-enduring mystery. Take the animations above. They show the flow that develops between two plates moving in opposite direction that are separated by a small gap. (The formal name for this is planar Couette flow.) The visualization is taken in a plane at a fixed height between the plates.
Initially (top), the flow shows narrow bands of turbulence, shown in green, separated by calmer, laminar zones in black. As time passes, these areas of laminar and turbulent flow self-organize, eventually forming diagonal stripes that are much longer than the gap between plates (bottom), the natural length-scale we would expect to see in the flow. Researchers have wondered for years why these distinctive stripes form. What sets their spacing, and why are they along diagonals?
To answer those questions, researchers explored the full Navier-Stokes equations, searching for equilibrium solutions that resemble the striped patterns seen in experiments and simulation. And for the first time, they’ve found a mathematical solution that matches. What the work shows is that the pattern emerges naturally from the equations; in fact, given the characteristics of the solution, the researchers found that many disturbances should lead to this result, which explains why the pattern appears so frequently. (Image and research credit: F. Reetz et al., source; via phys.org; submitted by Kam-Yung Soh)
June 11, 2019
An Introduction to Turbulence
With some help from Physics Girl and her friends, Grant Sanderson at 3Blue1Brown has a nice video introduction to turbulence, complete with neat homemade laser-sheet illuminations of turbulent flows. Grant explains some of the basics of what turbulence is (and isn’t) and gives viewers a look at the equations that govern flow – as befits a mathematics channel!
There’s also an introduction to Kolmogorov’s theorem, which, to date, has been one of the most successful theoretical approaches to understanding turbulence. It describes how energy is passed from large eddies in the flow to smaller ones, and it’s been tested extensively in the nearly 80 years since its first appearance. Just how well the theory holds, and what situations it breaks down in, are still topics of active research and debate. (Video and image credit: G. Sanderson/3Blue1Brown; submitted by Maria-Isabel C.)
November 12, 2018
Turbulent Volcanic Plumes
Volcanic eruptions produce some of the largest flows on Earth. These towering ash clouds were imaged from orbit in May 2017 as an eruption began on Alaska’s Bogoslof Island. The clouds are a beautiful example of a turbulent flow. Turbulence is characterized by its many length scales. Some features in the plume are tens or hundreds of meters across, yet there are also coherent motions down at the centimeter or millimeter scale. In a turbulent flow, energy cascades from these very large scales down to the smallest ones, where viscosity is significant enough to dissipate it. This is part of the challenge of modeling turbulence; to fully describe it, you have to capture what happens at every scale. (Image credit: DigitalGlobe, via Apollo Mapping; submitted by Mark S.)
November 30, 2017
Flow Above the Treetops
As this smoke visualization shows, trees have a significant impact on airflow around them. Flow in the image is from left to right. On the left, the upstream air is traveling in smooth, laminar lines that are quickly disrupted as the flow moves into the trees. After the first shorter trees, flow inside the wooded area has been broken up and slowed. Above the canopy, the smoke streaklines have also slowed and become more turbulent. Understanding how wind and trees interact is important in a variety of applications, including when adding renewable energy options to buildings and when predicting the spread of forest fires. (Image credit: W. Frank et al.)
May 2, 2017