What exact speed point does shock wave start to appear

[cjl]

Ahh, I seem to have found the paper I had remembered (and it's from one of my professors too, which explains why I saw it in the first place):

http://rd.springer.com/article/10.1007/BF02511381

 

[Aero_UoP]

and right on time. I was studying about shock tubes just now and I needed extra examples! xD
Thanks!

 

[boneh3ad]

And there we go: Van der Waals gas. I'm not even familiar with that sort of equation of state, but that seems to be about the sort of tomfoolery required to create an expansion shock.

 

[samsam18200]

Correct me if I'm wrong I'm only 15. But doesn't air pressure affect the speed at which is needed to make a cone. If so it would be easier at 50k feet to go faster but you would not created a cone until you reach a higher speed. And vice versa with say. 5k feet.