Maxhiker14
Active Member
I was looking at pictures from a rocket I flew a couple years ago and it reminded me of a question I've been wondering about for a while.
Just aft of the nozzle the exhaust appears straight and clean, then several inches further down the flame changes character completely, becoming brighter and much wider. What causes this and why do we see it on some motors but not others?
My best guess is that is has something to do with the exhaust being under-expanded at the nozzle exit, but it's not clear to me why the expansion happens further downstream.
Just aft of the nozzle the exhaust appears straight and clean, then several inches further down the flame changes character completely, becoming brighter and much wider. What causes this and why do we see it on some motors but not others?
My best guess is that is has something to do with the exhaust being under-expanded at the nozzle exit, but it's not clear to me why the expansion happens further downstream.