The (single) Merlin 1D vacuum engine's exhaust plume has a symmetric shape, comprising of six distinct "inner" plumes. Why does it have this shape?

Is it due to the shape/configuration of fuel injectors, or does the turbopump exhaust shape the plume somehow? Or something else entirely?

As seen during the recent SAOCOM 1a launch:

  • 3
    $\begingroup$ I believe it’s due to the configuration of the pintle injectors, but it’s hard to be sure since the schematics aren’t public $\endgroup$
    – Jack
    Oct 9 '18 at 9:21
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    $\begingroup$ Turns out that Scott Manley has a video on the SAOCOM launch and he thinks this is due to the slit-type pintle injectors producing uneven pressure areas. Also, from his video it seems the "inner plumes" aren't actually symmetric. $\endgroup$
    – czert
    Oct 9 '18 at 10:18

Scott Manley did a video on this from SAOCOM.

It basically seems to be some characteristic of the pintle injectors inside the engine, which leads to the unusual shape seen in the rocket plume. See his video for more details.

  • $\begingroup$ Yeah, see the comments to my question. Still, I'll leave this unanswered, as this is just Scott's opinion. Maybe, some time in the future, we'll know for sure. $\endgroup$
    – czert
    Mar 28 '19 at 13:09

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