Featured Presentations: Division of Fluid Dynamics Annual Meeting 2023

Wildfire Smoke Dispersion Can Be Tracked Accurately Using an Autonomous Drone Swarm System
November 19, 8:26-8:39 a.m. ET, Room 147A

Smoke pollution from wildfires can severely degrade air quality, imposing significant public health risks for populations living near the source. So far, researchers have struggled to accurately measure smoke dispersion during wildfires, making it difficult to predict how and where smoke pollution will spread. In this talk, researchers will introduce a system of autonomous drones, each of which uses digital holographic sensors and machine vision to track the composition and concentration of smoke in real time. The team demonstrated the swarm system’s capabilities via a drone deployment in Cedar Creek, Minnesota, and in simulations that recreated the environment there. As the threat of wildfires continues to grow, the new platform could transform future efforts to predict air quality and mitigate the effects of air pollution from wildfire smoke, as well as other harmful airborne pollutants.

New Theory Predicts Size Range of Raindrops When They Hit the Ground
November 19, 8:39-8:52 a.m. ET, Room 146A

Rain is a natural phenomenon experienced ubiquitously around the world. It can signal the change of seasons, bring relief during periods of drought, and spell disaster in flood-prone areas. Despite the pervasiveness and importance of rain in everyday life, scientists are still trying to figure out some of the most basic elements of its formation — like what determines the range of sizes of raindrops. For this presentation, scientists will describe a new theory to predict the sizes raindrops have for different rain intensities. By considering a thermodynamic energy balance combined with fluid dynamic processes, the team was able to determine the possible raindrop sizes just as they hit the ground. These new insights could have practical relevance for more accurate representations of rain in weather forecasts and climate models.

Ship Hull Roughness on a Tanker Substantially Increases Drag, Contributing to Shipping Industry Emissions
November 19, 9:18-9:31 a.m. ET, Room 143A

Every day, the shipping industry uses fleets of tankers and container ships to transport raw materials and goods across major waterways. Fuel consumption from all shipping fleets combined is thought to account for around 3% of global CO2 emissions. Much of these emissions derive from the energy needed to overcome hydrodynamic drag of the hull, the majority of which is caused by skin friction, even for a perfectly smooth hull. Drag from skin friction can more than double due to fouling from algae, barnacles, and other marine organisms. In this talk, researchers will describe new in-situ measurements of the fluid flow around a freshly cleaned and recoated vessel, indicating that even for a “clean” hull, drag was already 20% higher than for a perfectly smooth one. The findings highlight the need to improve cleaning practices and painting procedures to reduce hull drag, which could significantly reduce fuel usage, and thus the shipping industry’s environmental impacts and emissions.

Flow Visualization Inside a Centrifuge Offers Insights About Liquid Separation in the Kitchen and Lab
November 19, 3:26-3:39 p.m. ET, Room 158AB

Centrifuges are fast-spinning machines used to separate liquids of different densities in laboratories and kitchens alike. These vessels make use of centrifugal forces from fast rotation to push heavier liquids away from the center, allowing chefs to remove excess water from sauces and purees and enabling laboratory technicians to separate chemical samples. Recently, artist Maurice Mikkers equipped a centrifuge with a tiny camera to record this separation process for various liquid concoctions — footage which he shared on his YouTube channel, The Centrifuge Camera Channel. In this talk, scientists will show some of this surprising footage, along with experiments and simulations that elucidate the role of the centrifugal and Coriolis forces in the puzzling flow that can be observed inside the centrifuge tubes. The talk could offer practical tips for centrifuge users, such as chefs seeking to separate liquids to concoct sauces with the optimum consistency.

Cerebrospinal Fluid, Not Blood, Causes Enduring Tissue Damage After Brain Trauma
November 19, 4:35-5:01 p.m. ET, Room 209BC

During stroke, cardiac arrest, and other brain injuries, an accumulation of fluid in the brain causes severe swelling known as brain edema, which can lead to irreversible tissue damage. Most experts have believed that brain damage from edema is the result of blood rushing into the brain, but in this invited presentation, Douglas Kelley will describe recent findings in mice that challenge this notion. Imagery of fluid flow in the brain during a stroke showed that brain swelling in the first few hours of edema was caused not by blood, but by cerebrospinal fluid — a liquid found in the brain and spinal cord that normally serves to protect and detoxify the brain. The findings could transform the approaches doctors use to treat brain edema in the future to enable swifter recovery times and fewer complications after severe brain trauma.

Eel-Like Fish Continues Swimming After SpinalInjury by Amplifying Its Neural Feedbacks
November 19, 5:27-5:40 p.m. ET, Room 209BC

Spinal injuries in mammals often cause a permanent loss of function, severely hampering the ability for normal movement. Other vertebrates, like the lamprey — an eel-like fish — can continue swimming even after its spine has been injured. One hypothesis for this phenomenon is that lampreys compensate for loss of swimming function by amplifying neural processes that control their ability to sense changes to the body and adjust signals to their muscles. In this talk, scientists will describe model results that show how lampreys with disrupted spinal function amplify neuromechanical body-sensing feedback to continue swimming at near-normal performance. The model, which integrated neuromechanical and fluid dynamic processes, showed that amplified feedback in the injured region caused the swimmer to support the existing waves of motion that propagated through its body, allowing it to stabilize its swimming patterns.

Tiny Drones Offer an Inexpensive Platform for Measuring Atmospheric Airflow
November 19, 6:19-6:32 p.m. ET, Room 147A

Researchers have been trying to find more practical and inexpensive ways to measure large-scale wind flow patterns in the atmosphere, like flows downstream of buildings and wind turbines. Particle velocimetry, which involves tracing individual particle movement, is commonly used to measure airflow. But this technique has generally only been applied to centimeter-scale flow, while atmospheric flows occur at scales from hundreds to thousands of meters. For this presentation, scientists will introduce LaDrone, a new particle velocimetry technique that employs lightweight, GPS-tracked drones to collect 3D velocity measurements as they drift freely through the wind. Swarms of such drones, each weighing about 30 grams, could enable more practical assessments of near-surface atmospheric flow patterns that impact environmental processes, like the dispersion of airborne contaminants in urban environments.

New Modeling Results Aim to Describe Physical Conditions Responsible for Chronic Sinus Issues
November 20, 8:52-9:05 a.m. ET, Room 140B

The paranasal sinuses are sites of mucus production situated inside the skull, around the nose region. These are lined with tissues containing hair-like filaments called cilia. The cilia are responsible for clearing mucus from the sinuses, but for as much as 12% of the general population, this process can go awry, leading to diseases like chronic rhinosinusitis. In this talk, researchers will present a fluid dynamics model that recreates this mucus clearance process in the sinuses. The team identified that mucus clearance is dictated by a competition between two physical effects: gravity holding the mucus in, and mucus drainage caused by the cilia. By identifying the physical conditions that control mucus transport in the sinuses, these findings could inform better diagnoses and treatments for chronic rhinosinusitis.

Moving Wind Turbine Power Generation Can Be Enhanced in Unsteady Wind Conditions
November 20, 2:55-3:08 p.m. ET, Room 101

Floating offshore wind turbines are designed to capture wind energy while floating on the ocean surface. But the rocking movement of these turbines can introduce unsteady inflows of wind, which could jeopardize the turbines’ ability to capture wind power efficiently. Researchers have been investigating ways to leverage the motions of these turbines to achieve increased power generation relative to their fixed-bottom counterparts, but it has been difficult to describe these flow dynamics and potential mechanisms that could be employed for optimization. In this talk, researchers will provide a framework for assessing how much power can be extracted from turbines in unsteady wind conditions, using observations from a moving turbine in a wind tunnel. The findings could help guide designs for floating offshore wind farms currently being considered for development, including along the West Coast of the United States.

Red Tailed Hawks Pitch Their Wings Downward to Maneuver in Gusty Conditions
November 20, 3:21-3:34 p.m. ET, Ballroom A

Flight turbulence occurs when aircraft fly through wind gusts, pushing pilots off course and making it difficult for them to regain control. Some researchers have turned to birds for inspiration to develop new approaches for small-scale aircraft to more efficiently navigate gusty environments. Large birds are known to cope well with gusts, morphing the shape and orientation of their wings to maintain stability. In this presentation, scientists will show how a red-tailed hawk methodically steers through gusts. In response to an upward gust across its wings, the hawk rapidly pitched them downward at a steep angle to mitigate the additional lift or prevent stall due to the gust. This maneuver, along with tail pitching and rolling motions, helped the hawk to quickly reclaim stability. The strategy was recreated in a flight dynamics model, which accurately predicted the bird’s flight path only under the lower gust magnitude conditions. It failed to predict the flight path at higher gust magnitudes. In the future, these findings could help researchers design uncrewed aerial vehicles that are more resilient to adverse aerodynamic environments.

Vapor Bubbles Can Be Used to Propel Their Container Upward
Poster Session, November 20, 3:34-4:25 p.m. ET, Exhibit Hall D

Vapor bubbles are increasingly used in microfluidic systems for a variety of applications, from targeted drug delivery to water treatment. In bubble-based actuation systems, microbubbles and nanobubbles can be generated at controlled sizes and frequencies to manipulate fluid behavior. But most studies have focused on using bubbles to move fluid in a microsystem, not to move the system itself. In this poster presentation, researchers will show how vapor bubbles generated by hot oil in a beaker of water can make the whole beaker jump. Oil splashes are usually a nuisance for cookers, but in Hosokawa’s experiment, the oil vaporized water at the bottom of the beaker, generating vapor explosions that caused the whole system to jump and jolt. This contactless and controllable method could be used to drive microsystems for a range of uses.

Golden Eagles Use Intermittent Updrafts to Stay Aloft More Effectively
November 20, 4:25-4:38 p.m. ET, Room 140B

Large birds are known to morph their wings to resist or mitigate the effects of wind gusts, but new observations of accelerations in flying golden eagles might prove that these birds use gusts to their benefit. In this talk, researchers will describe how six golden eagles appear to amplify turbulence in intermittent updrafts as they flew through gusty winds, potentially exploiting the unsteady airflow to rapidly accelerate upward without expending too much energy. The observations demonstrate how these eagles might “play” with turbulence to glide through the air and stay aloft more effortlessly, rather than trying to mitigate its effects as other birds are known to do. The findings may help researchers to design similar sized uncrewed aerial vehicles that could perform such maneuvers, which may help them fly more efficiently.

Microfluidic Patch Driven by Wearer’s Pulse Can Deliver Drugs at a Constant Rate
November 20, 5:30-5:43 p.m. ET, Room 201

Using infusion pumps and syringe injections to deliver drug treatments like insulin and chemotherapy across the skin can be painful or disruptive, cause infections, and interfere with patient activity. For this reason, many researchers have been trying to develop less invasive ways to deliver these drugs through the skin, like transdermal patches. In recent work, researchers developed a microfluidic patch to deliver insulin into the skin, inspired by the principles of insect respiration. The patch, driven by the wearer’s pulse, could pump drugs into the skin without the use of external power, but consistent drug delivery remained challenging. In this talk, researchers will describe advancements to this design that allow the patch to deliver drugs consistently with carefully controlled delivery rates. Injection rates achieved by the patch were suitable for the delivery of both insulin and chemotherapy drugs. The concept could be put into commercial use to avoid complications from the use of syringes and powered infusion pumps for a variety of drugs.

Tiny Scales on Monarch Butterfly Wings Were Recreated to Reduce Drag
November 20, 5:30-5:43 p.m. ET, Room 146C

Monarch butterflies travel longer distances than any other insect, migrating more than 4,000 kilometers every year from the United States and Canada to Mexico and back again. When flapping their wings, monarchs can fly at speeds of up to five meters per second — an impressive feat for such a small insect. The butterfly’s wings, although relatively short and broad, are also covered in over a million tiny scales, each about 0.1 millimeters in size, which enhance their flying efficiency, among other functions. In this talk, scientists will describe an experiment where these scaly wings were recreated using plates with grooved surfaces, which reduced the plates’ drag by over 26%. Flow visualization showed how friction from air flowing over the grooved cavities created tiny vortices very close to the surface, allowing the air to skip over it smoothly. This flow control method could inform future efforts to design more efficient next-generation small flying robots.

Some Solid Biological Materials May Possess Fundamentally Different Properties Thanks to Water
November 21, 9:05-9:18 a.m. ET, Room 156

Solid biological matter, like wood and hair, behaves differently when it absorbs moisture, often expanding or changing its rigidity. These porous materials can hold water molecules in gaps between other molecules, which endow some of them with unusual and dynamic properties. While “hydration forces” from embedded water molecules have been studied for decades, the impact of these forces on solid biological matter has been generally neglected. In this talk, researchers will present findings that could upend prevailing notions about what hydration does to solid biological materials. Bacterial spores from soil were “jammed” with water molecules due to the effect of the hydration forces, resulting in a material that was more elastic and fluid with fundamentally different properties than its unjammed form. The concept of hydration solids could be used to design materials that can dynamically adapt their properties, becoming soft, hard, or viscous on command.

Clumpy Supernova 1987A Remnants May Have Formed the Same Way That Airplane Contrails Break Up
Gallery of Fluid Motion, November 19 at 7 a.m. ET - November 21 at 11:30 a.m. ET, Hall D

Nearly 40 years ago, astronomers discovered the iconic Supernova 1987A about 168,000 light-years away from Earth. Supernova 1987A was the first star explosion sighting in almost 400 years that was luminous enough to be visible to the naked eye, which has inspired decades of intensive research to try to understand its evolution. All of this time, one feature of Supernova 1987A’s remnants has baffled researchers: the formation of clumps of gas and dust along its equatorial ring. In this poster, a scientist will propose a hydrodynamic mechanism common to airplane wakes that could finally explain what causes this feature, revealed by the new James Webb Space Telescope. Just as condensation trails left by airplanes break up into clumps due to vortex rings, gas and dust clouds in Supernova 1987A may be doing the same thing. The findings solve a key mystery about this renowned supernova, providing new insights about the physics governing star formation.

Simulations Show How Star Wars’ Millennium Falcon Could Glide to the Ground Safely if Its Engines Had Failed During Battle
Gallery of Fluid Motion, November 19 at 7 a.m. ET - November 21 at 11:30 a.m. ET, Hall D

The Millennium Falcon was a clunky but reliable fictional starship that played a critical role in the destruction of the second Death Star and the decisive victory of the Rebel Alliance during the Battle of Endor in Star Wars: Return of theJedi. In a poster, a researcher will imagine a scenario in which the Millennium Falcon’s powerful engines fail at an altitude of two kilometers, requiring the starship to glide at a steep angle of attack to reach the ground safely. Large eddy simulations showed that a 20 degree angle of attack would be ideal for the Millennium Falcon while gliding through the atmosphere, which would allow it to safely coast to the ground over 3.6 kilometers. Visualizations show spectacular flow separations downstream of the starship, demonstrating how fluid dynamics simulations can glean insights about optimizing performance even with poor aerodynamic designs.