Supersonic Standing Still: The Physics Behind Wind Tunnel Experiments

[Graven Image]

Consider a situation where you are standing still (with your feet chained to the floor) experiencing a horizontal windspeed of >340 m/s. Despite the fact that you are stationary relative to the earth, are you in fact supersonic since you are moving faster than the speed of sound relative to the air around you? If so, would you experience a sonic boom? This is assuming that you survive of course!

 

[mgb_phys]

You wouldn't experience a supersonic boom in the same way that a passenger in concord doesn't. The boom is the shock wave behind you passing a point.
In a wind tunnel there would be a staionary shockwave some distance behind the subject so there isn't a boom as such, unless you ran backward and forward past the point thewave hits the wall!

 

[rcgldr]

A shock wave develops at every leading surface edge of a solid exposed where the relative air flow is supersonic. I don't think it's possible to hear a shock wave when the observer is moving as fast as the shock wave, for example a chase plane flying within the shock wave of another plane (this is actually done for testing purposes) just experiences a large pressure differential within the shock wave, and wouldn't hear the "cracK" of a shock wave as experienced by nearby stationary observer, or a "boom" from an observer much farther away.

 

[LURCH]

However, an observer stationary wrt the wind in the tunnel (i.e. floating by on the wind like a feather) would perceive you passing by at high speed, immediately followed by a sonic boom.