I think a bright light reflected reflected from a projection screen (like for a slide show) will give you enough bright defused light to see the refraction differences from the shock waves in the plume. Anybody got an old slide projector and screen? You might have to do some processing tricks with the video to see the plume clearly, contrast and edge detection perhaps?
Ah, yes- I tried to get this set up at RotRock back in '98. The best cheap method is to get a sheet of Scotchlite or some such retroreflector, place it behind the plume, and illuminate it coaxially with the camera- just like a front-projection unit as used in video & movie production. I've checked out the effect with an 8x11 inch panel built up from strips of reflective tape and a flashlite held alongside my head- it shows the heat shimmers from a match remarkably well, and the density variations of a rocket plume will be dramatic. I also tried it with the flow from a simple air nozzle, and I could see the mach disks & mixing region. I never did manage to get the RRC test site crew to buy into it, though.
For best results, a half silvered mirror can be used to provide a truly coaxial light source, but that may be overkill. Maybe even two cameras and two lamps could be used with the same reflector panel to produce stereo images...
Okay, now I have to scrounge up the parts and try it with the teacart engine, although a high intensity flash might be needed in this case to wash out the visible plume. I'll post pics.
Doug
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