To start with: What is the Sound Barrier?
The “sound barrier” refers to the point at which an object travels at the speed of sound, also known as Mach 1. Sound travels as pressure waves through a medium like air, and its speed depends on factors like temperature and altitude. At sea level, the speed of sound is roughly 1,225 kilometers per hour (761 miles per hour). When an object approaches this speed, it encounters a dramatic increase in aerodynamic drag and turbulence—this phenomenon was once thought to be an impenetrable "barrier."Breaking the Sound Barrier - and making the Shockwaves visible
NASA employed schlieren photography to capture the groundbreaking air-to-air images showcasing the interaction of shockwaves generated by two supersonic aircraft flying in close formation. The image features two T-38 jets from the U.S. Air Force Test Pilot School, flying roughly 30 feet apart at speeds exceeding the sound barrier. As they cut through the air, their shockwaves—responsible for the familiar sonic booms heard on the ground—were visually recorded in stunning detail. Originally monochromatic, the image was later colorized to enhance its clarity and impact. This remarkable snapshot was part of a supersonic flight series aimed at deepening our understanding of how shockwaves interact both with the exhaust plumes of aircraft and with one another.
Supersonic Flight
Supersonic flight occurs when an aircraft travels faster than the speed of sound, typically at Mach 1 to Mach 5. Aircraft designed for this purpose, like the Concorde or military jets such as the F-22 Raptor, face unique challenges:- Shockwaves: As an aircraft flies supersonically, shockwaves form around it, affecting aerodynamics and creating drag.
- Heat: Friction with air molecules generates intense heat, necessitating special materials to withstand high temperatures.
- Efficiency: Supersonic speeds consume immense amounts of fuel, which is why supersonic airliners were eventually retired due to cost concerns.
...and because those photos are so fascinating, here is another one! Well done, NASA!
How does Schlieren Photography work?
Schlieren photography is a fascinating technique used to visualize changes in the density of transparent fluids like air. These density changes are often caused by variations in pressure, temperature, or shockwaves, such as those created by objects moving at supersonic speeds. Here's how it works:Key Principles
- Light Refraction: When light passes through a medium with varying density, it bends (refracts) because the speed of light changes slightly depending on the medium's density.
- Optical Setup: Schlieren systems use a point light source, mirrors, and lenses to make these tiny changes in the light's direction visible.
How it Works
- Light Source: A bright point source, like a small LED or laser, emits light that passes through a transparent medium.
- Mirror or Lens: A concave mirror or lens focuses the light into parallel beams, which then travel through the area of interest—such as the air around a shockwave.
- Density Disturbances: If there are changes in air density (e.g., due to a shockwave), the light passing through those areas will bend slightly.
- Knife Edge or Filter: At the focal point, a small obstruction (such as a knife edge) blocks part of the light. This enhances the differences in light intensity, making the refracted light stand out.
- Resulting Image: A camera captures the distorted light pattern, revealing the density gradients in the medium. These gradients appear as light and dark regions, showcasing phenomena like shockwaves or heat flow.
And here one last one. Hell, NASA, you rock!
Applications
Schlieren photography is widely used in:- Aerodynamics: To study shockwaves, airflow, and heat plumes around high-speed aircraft or rockets.
- Engineering: For visualizing heat and fluid flow in research and development.
- Science and Medicine: To observe gas dynamics, such as the movement of heated air around objects.
...just sayin'
MiGFlug managed to show the moment when the MiG-29 broke the sound barrier during a fighter jet passenger flight? Without Schlieren photography, but normal video cameras! Look carefully, can you see it?Questions connexes
What is the sound barrier?
The "sound barrier" is the point at which an aircraft reaches the speed of sound, Mach 1 — roughly 1,225 km/h (761 mph) at sea level. Approaching it, aircraft meet a sharp rise in drag and turbulence that early engineers feared was an impenetrable barrier, until it was first broken in 1947.
What is schlieren photography?
Schlieren photography is a technique that makes differences in air density visible, allowing otherwise invisible shockwaves around fast-moving objects to be photographed. NASA used an advanced air-to-air version to capture supersonic shockwaves streaming off jets in flight.
How did NASA photograph supersonic shockwaves?
NASA used schlieren imaging to photograph two T-38 jets from the US Air Force Test Pilot School flying about 30 feet apart at supersonic speed. The result showed how the shockwaves from the two aircraft interact — data that helps engineers design quieter supersonic planes.
What is a sonic boom?
A sonic boom is the loud, thunder-like sound created when an aircraft travels faster than sound, as its shockwaves reach the ground. Reducing this boom is a major goal of modern supersonic research, which is why visualising shockwaves, as in NASA's images, matters so much.
Why do engineers want to see shockwaves?
Visualising shockwaves shows exactly how pressure waves form and merge around an aircraft, guiding designs that produce softer booms. This research could one day allow overland supersonic flight, reviving an ambition not seen since fast jets like the SR-71 Blackbird.
Which aircraft first broke the sound barrier?
The Bell X-1, piloted by Chuck Yeager, became the first aircraft to break the sound barrier in level flight on 14 October 1947. That milestone opened the supersonic age and led to research machines like the rocket-powered X-15.
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