Researchers have flown the first aircraft designed to maneuver without conventional control surfaces like ailerons and flaps. Instead of changing the wing geometry to alter the lift on different parts of the craft, the UAV uses strategically placed jets of air along the wing to control its flight. The plane can also alter the direction of its thrust, not by turning the nozzle as is conventionally done, but by modifying the thrust vector by directing and firing a secondary jet into the exhaust. #
Tag: fluid dynamics
Steam Devils
The formation of the ethereal steam devil is quite similar to the formation of a fire tornado. In this case, the first frost of the season cooled air temperatures substantially below the temperature of the water of the lake, creating conditions for steam and for updrafts of rising, warmer air. A slight breeze across the lake is enough to create pockets of vorticity, which stretch due to the updrafts and intensify due to conservation of angular momentum. This creates the narrow spinning vortex filaments that pull steam up and dance across the lake’s surface. #
Wind Turbines and Weather
A new study reports that wind turbine farms may be changing local surface temperatures, resulting in warmer temperatures at night and cooler temperatures during the day. The result is neither surprising nor new; the motion of the propellers increases the turbulence downstream of the turbines. Turbulent flow mixes much better than laminar flow, so air from above the ground is getting mixed into surface air in the wakes. At night, the air next to the ground cools more quickly than air higher up, so the mixing of higher, warmer air results in localized warmer air on the ground. Orange farmers use this effect when they put out fans at night to keep their crops from freezing. #
Jupiter and the Kelvin-Helmholtz Instability
Jupiter, known for its colorful bands of stormy clouds, is a beautiful subject for fluid dynamics in action. As the planet turns, the cloud bands move at different relative speeds. This velocity difference at the interface of the bands can trigger the Kelvin-Helmholtz instability, resulting in a line of whorls where the cloud bands meet. The instability has been observed on Saturn and is thought to be fairly common among gas giants.
Non-Newtonian Fluids
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Non-Newtonian fluids have even made it into pop culture. #
Wingtip Vortices in Ground Effect
In this flow visualization, wingtip vortices from an aircraft have been simulated using an apparatus with a couple of flaps that snap together like a book closing. Dye is pooled on the “ground” below the flaps and gets entrained by the vortices and lit up using laser light. The red vortices are the primary vortex generated by the aircraft wingtips and the green ones are secondary vortices generated by interaction with the ground. The lower half of the picture is a reflection off the ground. This photo was part of the 2009 Gallery of Fluid Motion. #
Paper Plane Physics
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It’s a little surprising that this would be so stable, but I don’t have any reason to believe it impossible. #
Wild Ferrofluid Shapes
In this fluid experiment, a ferrofluid–typically a liquid with a suspension of ferric particles–is exposed to rotating magnetic fields, which results in some wild shapes. #
Benard Cells
When a fluid in a gravitational field is heated from below, it can develop a Rayleigh-Benard instability which causes the formation of convection cells as in the video above. The hexagonal shape of the cells is due to the boundary conditions of the fluid. It’s possible to form other shapes like spirals. The same mechanism drives the formation of granules on the photospheres of stars like our sun.
Human-Powered Ornithopter
A team at the University of Toronto has flown the world’s first human-powered ornithopter, an aircraft that flies by flapping its wings like a bird. The concept dates back all the way to Da Vinci in the 15th century. Part of why it’s taken centuries to realize the dream is that bird flight is much more complicated than simply flapping up and down. Flapping a wing up and down will produce lift equally upward and downward. In order to create usable lift and thrust, it’s necessary to change the angle of attack during each stroke by twisting the wing while flapping. Watch the U of T craft carefully, and you can see this happening. #
