How Insects Fly in the Rain

Getting caught in the rain is annoying for us but has the potential to be deadly for smaller creatures like insects. So how do they survive a deluge? First, they don’t resist a raindrop, and second, they have the kinds of surfaces water likes to roll or bounce off. The key to this second ability is micro- and nanoscale roughness. Surfaces like butterfly wings, water strider feet, and leaf surfaces contain lots of tiny gaps where air gets caught. Water’s cohesion — its attraction to itself — is large enough that water drops won’t squeeze into these tiny spaces. Instead, like the ball it resembles, a water drop slides or bounces away. (Video and image credit: Be Smart)

#biology #butterfly #cohesion #droplets #fluidDynamics #hydrophobic #insects #physics #science #superhydrophobic #surfaceRoughness #surfaceTension

Many industrial processes, including those producing aluminum and “green” hydrogen, use electrodes to speed up chemical reactions. Unfortunately, bubbles that form on the electrode reduce its efficiency anywhere from 10 to 25 percent by blocking parts of the electrode. The assumption has been that any area shadowed by bubbles is blocked, but a recent study shows that’s not the case. Instead, it’s only the electrode area in direct contact with the bubble that’s blocked.

To show this, researchers looked at a smooth electrode where bubbles formed randomly (left) and a nanotextured one with many spots where bubbles could form (right). In the animation above, bubble shadows are highlighted with circles. There are clearly more bubbles on the nanotextured electrode, but it actually performs better than the smooth electrode because the bubble contact area is smaller. (Image and research credit: J. Lake et al.; via MIT News)

https://fyfluiddynamics.com/2024/11/blocking-bubbles/

#bubbles #chemistry #fluidDynamics #nanoscale #nucleation #physics #science #surfaceRoughness

Growing up in northwest Arkansas, I spent my share of summer nights sheltering from tornadoes. Central North America — colloquially known as Tornado Alley — is especially prone to violent thunderstorms and accompanying tornadoes. That’s due, in part, to two geographical features: the Rocky Mountains and the Gulf of Mexico. Trade winds hitting the eastern slope of the Rockies get turned northward, imparting a counterclockwise vorticity. At the same time, warm moist air carried from the Gulf feeds into the atmosphere, creating perfect conditions for powerful thunderstorms. By this logic, though, South America should see lots of tornadoes, too, courtesy of the Andes Mountains and the moist environs of the Amazon Basin. To understand why South America doesn’t have a Tornado Alley, researchers used global weather models to investigate alternate North and South Americas.

They found that smoothness is a key ingredient for the upstream, moisture-generating region. Compared to the Amazon, the Gulf of Mexico is incredibly flat. With a flat Gulf, tornadoes abounded in North America, but their numbers dropped once that area was roughened to mimic the Amazon. The opposite held true, too: a smoothed-out Amazon Basin resulted in more simulated South American tornadoes.

For those in Tornado Alley, the results don’t offer much hope for mitigating our summer storms — we can’t exactly roughen the ocean. But the study does sound a word for warning for South America; the smoother the Amazon region becomes — due to mass deforestation — the more likely tornadoes become in parts of South America. (Image credit: G. Johnson; research credit: F. Li et al.; via Physics World)

https://fyfluiddynamics.com/2024/08/why-tornado-alley-is-north-american/

#atmosphericScience #CFD #computationalFluidDynamics #fluidDynamics #meteorology #physics #science #surfaceRoughness #thunderstorm #tornado #vorticity

Some of the differences between beach volleyball and indoor volleyball are obvious, like the number of players allowed — two versus six — and the courts — a smaller sand court versus a bigger indoor court. But there are subtle and significant differences in the balls themselves. Both beach and indoor volleyballs used for competition are required to weigh between 260 and 280 grams, but the expected diameter of the balls differs by about 1 centimeter, with beach volleyballs coming out slightly larger. The balls differ in their surface roughness, too, with indoor models being smoother, even before in-game wear.

Although these differences seem minor, they can make a significant impact in the game. Volleyball regulations don’t specify a ball’s expected surface roughness or how many panels they should be made with. As in football, these seemingly cosmetic changes can strongly affect airflow around the ball and change its trajectory. Regulations require that all balls used in a given match be uniform, but that still requires athletes to potentially adjust to the behavior of a new ball at each competition. (Image credits: I. Garifullin, C. Chaurasia, C. Oskay, and M. Teirlinck)

Related topics: How smoothness and panel design affect a football, volleyball aerodynamics, and vortex generators on cycling skinsuits

For more ongoing and past Olympic coverage, click here.

https://fyfluiddynamics.com/2024/08/paris-2024-beach-versus-indoor-volleyballs/

#aerodynamics #beachVolleyball #dragCrisis #fluidDynamics #olympics #Paris2024 #physics #science #sport #surfaceRoughness #volleyball

Soft materials tend to be sticky, and once they’re adhered to a surface, they’re often harder to remove than they were to attach — think of Scotch tape stuck to a desk. This difficulty separating sticky things — known as adhesion hysteresis — has been attributed to various causes, like energy lost to viscoelasticity or age-related chemical bonding. But a new study shows that both those explanations are unnecessary.

Instead, the difficult removal comes from the way two surfaces separate in fits and starts. No two surfaces are perfectly smooth, and soft surfaces are able to conform to all the nooks and crannies of their partner surface. That molding results in a lot of surface contact, all of which must break for the materials to detach. That peeling doesn’t take place smoothly. Instead, the two surfaces part a little at a time in discrete jumps, as shown in the image above. The colors in the illustration show how much energy is dissipated in each jump, with darker colors indicating higher energy. The team found that this stick-slip mechanism is enough to account for the struggles we have un-sticking objects. They’re now looking at how water affects these narrow meeting places between sticky surfaces. (Image and research credit: A. Sanner et al.; via Physics World)

https://fyfluiddynamics.com/2024/05/unsticking-in-jumps/

#adhesion #fluidDynamics #physics #science #solidMechanics #stickSlip #surfaceRoughness