NASA NASA Captures First Air-to-Air Images of Supersonic Shockwave

[Spinnor]

https://www.nasa.gov/centers/armstrong/features/supersonic-shockwave-interaction.html

“We never dreamt that it would be this clear, this beautiful.”

Physical Scientist J.T. Heineck of NASA’s Ames Research Center in Mountain View, California gets his first glimpse at a set of long-awaited images, and takes a moment to reflect on more than 10 years of technique development – an effort that has led to a milestone for NASA’s Aeronautics Research Mission Directorate.

NASA has successfully tested an advanced air-to-air photographic technology in flight, capturing the first-ever images of the interaction of shockwaves from two supersonic aircraft in flight.

“I am ecstatic about how these images turned out,” said Heineck. “With this upgraded system, we have, by an order of magnitude, improved both the speed and quality of our imagery from previous research.”

 

[Greg Bernhardt]

Very cool! Is the technology only for still photos or could there be video at some point?

 

[boneh3ad]

You can do schlieren videos, though I am not sure how well it would work in a situation like this where the background pattern is in motion. Background oriented schlieren (BOS) requires a static background image with no flow disturbances as a reference in order to work. The idea is you take that background with some kind of pattern on it that allows reliable cross-correlation. Then you take another image with the flow process occurring in front of the background. The shock and expansion waves mean there will be density gradients that bend light and distort the background image. By cross-correlating the baseline and distorted images (or, rather, subsets of them), you can work out the density gradient, which is what is pictured in these photos.

In principle, once you have a single reference background image, you could then take a movie of the planes flying over it provided the background was effectively stationary, so parallax is our friend here. You'd need to be at a high enough altitude that it appeared stationary over the time scales involved, but not so high that it just looks like a smeared blur, as you need texture to that background to do the cross-correlation.

 

[Klystron]

The T-38 Talon in the schlieren photos also cool and amazing. This aircraft was the go-to trainer back in the 1970's after setting numerous records for supersonic flight in the 1960's. Love this T-38 photo over Edwards AFB. NASA has similar models for chase and research.

You can do schlieren videos, though I am not sure how well it would work in a situation like this where the background pattern is in motion. Background oriented schlieren (BOS) requires a static background image with no flow disturbances as a reference in order to work. The idea is you take that background with some kind of pattern on it that allows reliable cross-correlation. Then you take another image with the flow process occurring in front of the background. [snip]

The hypersonic wind tunnel, part of the Unitary Plan wind tunnel complex at NASA Ames research center, had a thick 'schlieren window'. If memory serves one could view transitions then the shock wave passing as operations exceed mach 1. The window was usually obscured by camera equipment during experiments but was unencumbered during site acceptance testing after new drive motors installed.

 

[boneh3ad]

That's probably a Z schlieren system, though. BOS is relatively new since it requires digital image analysis. Z schlieren can be done entirely analog.

 

[Andy Resnick]

https://www.nasa.gov/centers/armstrong/features/supersonic-shockwave-interaction.html

Whoa.. that's awesome! Thanks for the link!

 

[boneh3ad]

These images will be going on up a screen in my compressible flow class as soon as the students return from spring break on Monday. We literally just finished covering oblique shocks and expansion waves.

 

[sysprog]

... when I was in the USAF way back in the 1970's after setting numerous records for supersonic flight in the 1960's

Wow. You and Col. Yaeger at each other's heels like that. Cool.

 

[Klystron]

Wow. You and Col. Yaeger at each other's heels like that. Cool.

The aircraft set the records. I was but a child. I'll edit the sentence . Yeager began as an enlisted maintenance tech then flyer during WWII. His highest rank was General in the USAF, though he was a colonel while commanding a squadron IIRC.

 

[sysprog]

The aircraft set the records. I was but a child. I'll edit the sentence . Yeager began as an enlisted maintenance tech then flyer during WWII. His highest rank was General in the USAF, though he was a colonel while commanding a squadron IIRC.

Oh c'mon, Klystron -- I was just razzin' about the amphiboly in the sentence --
If you edit it to fix it you'll ruin the fun ...

... and you do recall correctly ... Gen. Yaeger was Col. Yaeger in the '60s ...