Nasa captures images of supersonic shockwaves | Hacker News Reader

Nasa captures images of supersonic shockwaves

phys.org

63 pointslelf17 comments

As mentioned by others, the photography technique looks like (and apparently is a software enabled variant of) Schlieren photography. This(1) is a neat example of an old school Schlieren set up capturing shockwave formation during whip cracks. I highly recommend it.

(1) https://www.youtube.com/watch?v=AnaASTBn_K4

Very cool. They didn't mention this in the video, but I immediately see one groundbreaking new phenomenon that they uncovered: at the exact moment the end of the whip goes supersonic, it is being accelerated by something other than the tension of the rope. It looks as though it's accelerated by the shockwaves, of which there appear to be two -- one on each side of the whip end, with a vacuum in between. It's as clear as day in the video. The rope in front of it clearly goes lax, and the whip end even changes direction to align with the shock wave propagation.

I thought about this and watched the video again, and I've changed my mind just a bit. It looks like, instead of being accelerated, the whip end is experiencing reduced drag in the vacuum between the two shock waves. We can see that it travels right behind the first shockwave, not lagging at all, and this is exactly what you would expect if it is both the source of the shockwave and the beneficiary of the vacuum behind it.

How are these images captured? They look like Schlieren photography, but as I understand it that requires a mirror on the other side of the target being photographed.

It is a Schlieren technique, but in this case a series of images taken over a textured background are then processed with software in a way that amplifies the differences in air density. This page goes into a little more detail:

https://technology.nasa.gov/patent/TOP2-271

Thank you, that's really interesting!

Someone posted this [0] on an article from another website. It's NASA's method for taking these sorts of pictures from the ground. The process for taking airborne images is probably similar, but must require so much more coordination.

[0] https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201700...

More on NASA's attempt to solve "quiet" supersonic flight.

https://www.nasa.gov/QSF18

Anyone found hi-res versions of these images?

NASA has somewhat larger versions linked on this article, though they aren't really sufficient for larger wallpapers or prints:

https://www.nasa.gov/centers/armstrong/features/supersonic-s...

The photos aren't yet listed in their image database[0], unfortunately. They also publish[1] high-resolution versions on Flickr, so it's possible the photos might make their way there in the near future. Alternatively, they give a phone number (202-358-1900) to inquire about media use of specific images.[2] Maybe I'll give them a call later if someone doesn't beat me to it. Or the high-res photos will make their way onto Flickr, since they already posted to Instagram as of yesteray.

0. https://nasasearch.nasa.gov/search/images?affiliate=nasa&que...

1. https://www.flickr.com/photos/nasahqphoto/

2. https://www.nasa.gov/multimedia/guidelines/index.html

I came here to ask this!

I really wonder who makes the decision of starting work on this kind of research, and how it goes.

I hope it's not in the lines of "Alright team, we've got two idle supersonic jets, a high speed camera, and enough jet fuel to burn for a day, so how about some ideas?"

It’s probably “we now have two idle supersonic jets”. Everything else they already had. And good budget planning always helps.

> It’s probably “we now have two idle supersonic jets”.

It's likely not. This kind of thing takes a lot of planning and coordination.

I suspect the idea of quiet supersonics are also very interesting to the Department of Defense as well (for relatively obvious reasons).

I wish there were video :(

NASA is a an acronym and not a word

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