A non-cylindrical stream falling through a slit nozzle exhibits the Plateau-Rayleigh instability, which drives a falling jet of fluid to break into droplets due to surface tension. The fingers formed off the falling stream may be a form of Rayleigh-Taylor instability. #
Search results for: “jet”
Jets from Waves
When vibrated, fluid surfaces can exhibit standing waves known as Faraday waves. In this experiment, increased forcing of these standing waves causes the formation of a jet. Under the right conditions, as the standing wave collapses, a singularity forms on the fluid surface when velocity and surface curvature diverge. The narrow jet column forms as a result of the fluidโs kinetic energy getting focused by the collapse. For more, see this letter to Nature. #
Instability in a Jet
This photo shows the development of a flow instability in an axisymmetric jet. On the left, the jet is smooth and fully laminar, but, by the center of the photo, disturbances in the jet have grown large enough to distort the laminar profile. The jet is then in transition; by the right side of the frame, it has reached a turbulent state, as evidenced by the increased mixing (which causes the smoke to disperse more quickly) and intermittency of the flow. #
Jet-Based Control
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. #
The Bouncing Jet
Under some circumstances, a thin stream of a Newtonian fluid impacting a deep pool of the same fluid can produce a bouncing jet. The effect is observed in common liquids like canola oil and can be replicated at home. Be sure to check the research page for a video of the effect. #
Seeking Quieter Supersonic Flight
Supersonic flight over the U.S. has been banned by all non-military aircraft for more than fifty years. The ban gained momentum in the 1960s after test programs over St. Louis and Oklahoma provoked public outcry. But NASA’s X-59 aircraft is working to lift the ban by softening the sonic booms that encouraged the ban in the first place. Although it hasn’t been tested at supersonic speeds yet, pilots are putting the sharp and skinny X-59 through its paces, slowly widening the flight envelope.
In the video above, NASA shares footage of some of the recent test flights, including various maneuvers like phugoids, banking rolls, flutter, and landing gear tests. Pay close attention to the pilot’s view and the radio chatter, and you’ll hear that they’re hovering around Mach 0.98 in some cases–just underneath the point of generating a shock wave around the aircraft. It will be neat to see what happens when they finally do go supersonic. Will it be as quiet as promised? (Video credit: NASA; image credit: NASA/L. Losey; see also NASA; via Gizmodo)
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Plucking Droplets
A sudden breeze can pluck droplets hanging from a stem. Here, researchers recreate that phenomenon in the laboratory. With a close-up view and high-speed images, we can enjoy every detail of the detachment and break-up. As the wire pulls away, it drags a liquid sheet off the droplet. The thicker rims on either side of the sheet eventually collide, creating a jet that stretches, deforms, and, at last, breaks. (Video and image credit: D. Maity et al.)
Animation of two droplets getting plucked, one made of glycerin+water (left) and one of water (right). Fediverse Reactions
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A Bubbly Heart
Next time you fill your water bottle, watch closely and see if you can spot a bubble heart like these. When a jet falls into a pool, it pulls air in with it. The low pressure of the jet pulls bubbles inward, even as shear pulls the bubbles downward with the sinking liquid. If the bubbles are large and there’s enough momentum in the jet, the lower portion of the bubble will get pulled into a conical shape, while the upper portion remains a hemisphere. That forms one lobe of the heart. The other half requires a second bubble. But with a little patience and luck, you can form a complete heart. Happy Valentine’s Day! (Image credit: S. Tuley et al.)
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Entraining Bubbles
Every time I fill a glass at my refrigerator, I watch how the falling jet creates a cloud of bubbles. The bubbles form when the impacting water jet pulls air in with it, though, as this video shows, the exact origins can vary. Here, researchers take a closer, slowed-down look at the situation; they connect disturbances in the jet and waves at its base to the entrained bubbles that form. (Video and image credit: S. Relph and K. Kiger)
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“500,000-km ย Solar Prominence Eruption”
It’s difficult at times to fathom the scale and power of fluid dynamics beyond our day-to-day lives. Here, twists of the Sun‘s magnetic field propel a jet of plasma more than 500,000 kilometers out from its surface in an enormous solar prominence eruption. To give you a sense of scale for this random solar burp, that’s bigger than ten times the distance to satellites in geostationary orbit. (Image credit: P. Chou; via Colossal)
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