Tag: experimental fluid dynamics

Testing Full-Size Engines
Engineers can often use small-scale models to test the physics of their creations, but sometimes there’s no substitute for going large. In this photo, we see a full-size commercial engine used on an airplane, mounted at the Instituto Nacional de Tecnica Aeroespacial (INTA) in Madrid.
Behind the engine, in red, is an optical rig used for a brand-new measurement technique that allows engineers to directly measure the carbon dioxide emissions of the engine as it runs. The optical frame is 7 meters in diameter and uses 126 beams of near-infrared laser light to probe the engine’s exhaust without interrupting the flow. It’s the first chemically specific imaging of a full-scale gas turbine like those found on commercial aircraft. Given the high carbon emissions associated with air travel, the technique will be important for engineers building greener aircraft engines. (Image and research credit: A. Upadhyay et al.; via The Engineer; submitted by Simon H.)
November 10, 2022
Optimizing Wind Farms Collectively
In a typical wind farm, each wind turbine aligns itself to the local wind direction. In an ideal world where every turbine was completely independent, this would maximize the power produced. But with changing wind directions and many turbines, it’s inevitable that upstream wind turbines will interfere with the flow their downstream neighbors see.
So, instead, a research team investigated how to optimize the collective output of a wind farm. Their strategy involved intentionally misaligning the upstream wind turbines to improve conditions for downstream turbines. They found that the loss in power generation by upstream turbines could be more than recovered by improved performance downstream.
After testing their models over many months in an actual wind farm, they reported that their methodology could, on average, increase overall energy output by about 1.2 percent. That may sound small, but the team estimates that if existing wind farms used the method, it would generate additional power equivalent to the needs of 3 million U.S. households. (Image credit: N. Doherty; research credit: M. Howland et al.; via Boston Globe; submitted by Larry S.)
September 29, 2022
Making Hurricanes
With oceans warming, there’s more energy available to intensify hurricanes. And while our weather models have gotten better at predicting where hurricanes will go, they’re less good at predicting hurricane intensity, largely because capturing real data from storms is so difficult and dangerous. To address that shortfall, engineers build facilities like the one seen here, which simulates hurricane wind and water conditions so that scientists can study their interaction and better understand storm physics. Check out the full Be Smart video for a tour of the facility and a look at their work. (Image and video credit: Be Smart)
July 13, 2022
When Seeing a Flow Changes It
Adding dye to a flow is a common technique for visualization. After all, many flows in fluids like air and water are invisible to our bare eyes. But for some classes of flows — especially those driven by variations in surface tension — adding dye can have unforeseen effects. A recent study shows how true this is for bursting Marangoni droplets, where evaporation and alcohol concentration can pull a water-alcohol droplet apart.
As more dye is added to the experiment, the daughter droplets grow larger and more ligaments form. In the first three images, a dashed black line has been added to show the location of the droplet rim.
Without dye, it’s nearly impossible to see the phenomenon since the refractive indices of the two component liquids are so close. But the researchers found that, as they added more methyl blue dye, it did more than increase the contrast in the flow. It changed the flow, making the droplets larger and creating ligaments between them. They believe that the dye’s own surface tension creates local gradients that alter the flow. It’s a reminder that experimentalists have to be careful to consider how our efforts to measure and observe a flow can change it. (Image credit: top – The Lutetium Project, bottom – C. Seyfert and A. Marin with modification; research credit: C. Seyfert and A. Marin)
June 21, 2022
Measuring Drag
After a noticeable rise in the prevalence of home runs beginning in 2015, Major League Baseball commissioned a report that found the increase was caused by a small 3% reduction in drag on the league’s baseballs. When such small differences have a big effect on the game, it’s important to be able to measure a baseball’s drag in flight accurately.
In the past, that measurement has often been done in a wind tunnel, but the mounting mechanisms used there result in drag measurements that are a little higher than what’s seen from video tracking in actual games. Now researchers have developed a new free-flight method for measuring a baseball’s drag. The drag measurements from their new method are lower than those for wind-tunnel-mounted baseballs and in better agreement with video-based methods. The authors’ method should be adaptable to other sports like cricket and tennis, which will hopefully provide new insight into the subtleties of their aerodynamics. (Image credit: T. Park; research credit: L. Smith and A. Sciacchitano; via Ars Technica; submitted by Kam-Yung Soh)
June 2, 2022
Acidic Aerosols
As ocean waves crash, they generate aerosols — tiny liquid and solid particulates — that interact with the atmosphere. Curious about the chemistry of these tiny drops, researchers set out to measure their acidity. That’s easier said than done. Over time, aerosol droplets acidify as they interact with acidic gases in the atmosphere and capturing fresh aerosols in the field is next to impossible.
To tackle these challenges, researchers instead moved the aerosols to the laboratory, filling a wave channel with seawater and agitating it to generate aerosols they could then measure. They found that the smallest aerosols become a million times more acidic than the bulk ocean in only two minutes! Find out more about their experiment and its implications over at Physics Today. (Image credit: E. Jepsen; research credit: K. Angle et al.)
May 31, 2022
Dune Invasion
Migrating sand dunes can encounter obstacles both natural and manmade as they move. Dunes — both above ground and under water — have been known to bury roads, pipelines, and even buildings. A recent experimental study looks at which obstacles a dune will cross and which will trap it in place. Their set-up consists of a narrow channel built in a ring, essentially a racetrack for dunes. Flow is driven by a series of paddles that rotate opposite the tank’s rotation.
The team studied obstacles of different shapes and sizes relative to their dunes, and they found that dunes were generally able to cross obstacles that were smaller than the dune. Obstacles larger than the dune would trap it in place, and, for obstacles close to the same size as the dune, round obstacles were easier to cross whereas sharp-angled ones tended to trap the dune.
The idealized nature of their experiment means that their results aren’t immediately applicable to the complex dunes of the outside world, but the study will be an important touchstone for those predicting dune behavior through numerical simulation. Studies like those require experimental cases to validate their baseline simulations. (Image credit: top – J. Bezanger, figure – K. Bacik et al.; research credit: K. Bacik et al.; via APS Physics)
November 23, 2021
The Acoustics of Stonehenge
Stonehenge has long been an astronomical wonder, but did you know it’s an aural wonder as well? A team of acoustic engineers and an archaeologist constructed and tested a 1:12 scale model of the monument as it existed around 2200 B.C. Their model included 157 3D-printed stones (which took about nine months to print!), carefully engineered to reflect ultrasonic frequencies the way the full-size Stonehenge reflects frequencies in our auditory range. (Using the higher frequency sound at a smaller physical scale allows engineers to match the physics of the real henge.)
The team found that the stones of the henge amplified sound by about 4 decibels, enough to make a speaker’s voice easy to hear, even when facing a different direction. The structure also provided some reverberation that would enhance musical instruments or singing. Stonehenge had reverberation levels similar to a modern-day large movie theater, which is absolutely incredible for a prehistoric structure constructed in the open air.
For more interesting details on the model’s construction and testing, check out this article at Physics Today. (Image and research credit: T. Cox et al.)
November 3, 2021
Tokyo 2020: Kasai Canoe Slalom Course
The Kasai Canoe Slalom Course is Japan’s first man-made whitewater venue. To test the design and its multiple configurations, engineers at CTU in Prague built this large-scale hydraulic model. Check out the video below to see it under construction and in action.

The course is adaptable so that it can be used for high-level competitions like the Olympics, then reconfigured for recreational use. You can even see what it’s like to run part of the course in a multi-person raft, thanks to a miniature, GoPro-equipped boat! (Image credit: top – M. Trizuliak, others – CTU Prague; video credit: CTU Prague)
Missed our previous Olympics coverage? Check out how sailboats outrace the wind, the future of swim tech, and how surface roughness affects volleyball aerodynamics.
August 5, 2021
Seeing Through
Often researchers are interested in flows around and between objects, but seeing those flows is a challenge in a crowded field of view. One useful trick for this problem is matching the refractive index of your objects and the fluid they’re immersed in. Here we see the glass beads in a container seemingly disappear when a mixture of water and ammonium thiocyanate is poured in. Now the researchers can use many different visual diagnostic techniques to observe the interior flow! (Image credit: Datta Lab, Princeton University, source)
May 13, 2021