Supersonic airflow in a rocket nozzle


That video has many similarities to some fractals I remember rendering when I was younger. In particular, I remember creating an animation of a Julia set fractal where each frame was a re-render of essentially the same fractal, with just the real part of the starting constant increasing slowly. But I don’t have that animation anymore.

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What you're looking at is a supersonic wind tunnel, which is pretty much shaped the same way as a rocket engine.

You want something like “exit nozzle” or “exhaust port” instead of “engine”.

Because rockets mostly have motors, not engines. Unless they are hybrids of some sort.

Apologies for the technitpiggling, but it’s actually a meaningful distinction & well within my field of expertise.

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I’m so hot right now. Quoting Thomas Pynchon’s Rocket Limericks from Gravity’s Rainbow:

There was a young fellow name Yuri,
Fucked the nozzle right up its venturi.
He had woes without cease
From his local police
And a hell of a time with the jury.

This isn’t actually in a wind tunnel. The title of the clips is “Rocket startup CFD”. CFD stands for Computational Fluid Dynamics, so this is a simulation.

Still way cool.

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Very interesting post.

That’s what I thought. It is the graphical output of a computer simulation.

As a youngster we used to go and watch fighter jets (Dassault Mirages) take off at night (I was an Australian airforce brat, way back when we were allowed down near the runway). I remember seeing evenly spaced vertical dark bars in the supersonic “flame” behind the engine as they put on full thrust including afterburner for take-off. I seem to recall that they were explained as standing shockwaves of some sort. Some sort of supersonic resonance. It was completely weird to see these stationary dark vertical lines in a roaring orange flame that you knew was far from stationary.


Those are called Shock Diamonds.

Thanks! That’s them. My half-remembered explanation wasn’t so bad after all.

My favorite ever launch to see was a B-1B taking off from Robins AFB in Georgia, full afterburner and loud enough to wake the dead. Pure awesome.
A supervisor of mine was a crew chief on the SR-71 back in the day, and while doing engine runs for maintenance (where the aircraft was secured to the tarmac and then engines were run up to some high degree of rated power) he would get large rocks from the airfield and throw them into the exhaust plume. The end result was holes in the blast fences 150 feet behind the aircraft and a Letter of Reprimand for my previous boss.


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