What are the unique characteristics of a scramjet exhaust plume?

[Flyboy]

Got a bit of a headscratcher for y'all.

What would the exhaust plume from a scramjet look like? Using the X-43 as an example because it's a well documented design.

I've found some stuff that seems to point towards looking like a mildly underexpanded rocket exhaust, but it's only a few images and a technical report (attached for fun).

Analytical/theoretical drawings

Test chamber

I can wrap my head around the circular plume design, because we see it so often, but the linear design of most scramjets I've seen is confusing me. And the above actual image is... Kinda confusing because it's hard to tell what's engine plume and what's disturbed airflow around the test stand.

Thoughts?

 

[Klystron]

While not specific to scramjets, I observed many different jet and rocket exhausts in my USAF and NASA days. Most exhaust plumes in the atmosphere after detaching from the nozzle, vessel or afterburner tend toward an acquired shape; i.e., a conical projection progressing to a cylinder.

This may be at least partially an artifact of human perception. Infra-red technology and special cameras reveal complex patterns within apparent laminar exhaust flows. With proper technology the OP can probably learn to distinguish scramjet exhaust from a similarly fueled jet engine by analyzing exhaust components and motions within the plume.