Supersonic Standing Still: The Physics Behind Wind Tunnel Experiments

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Discussion Overview

The discussion explores the concept of supersonic motion in a wind tunnel scenario, particularly focusing on whether a person standing still while experiencing a high horizontal windspeed (greater than 340 m/s) would be considered supersonic relative to the air and whether they would experience a sonic boom. The scope includes theoretical implications and interpretations of shock waves in fluid dynamics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if a person standing still in a wind tunnel with a windspeed over 340 m/s is supersonic relative to the air and whether they would experience a sonic boom.
  • Another participant argues that a sonic boom would not be experienced in the same manner as a passenger in a supersonic aircraft, noting that the shock wave would be stationary relative to the wind tunnel.
  • A different viewpoint suggests that shock waves develop at the leading edges of surfaces exposed to supersonic airflow, and that an observer moving with the shock wave would not hear it as a boom, contrasting with stationary observers who would.
  • One participant posits that an observer stationary with respect to the wind would perceive the high-speed individual passing by, followed by a sonic boom.

Areas of Agreement / Disagreement

Participants express differing views on the experience of sonic booms in relation to motion and shock waves, indicating that the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

The discussion involves assumptions about relative motion, the nature of shock waves, and the conditions under which sonic booms are perceived, which may not be fully articulated or agreed upon.

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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!
 
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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!
 
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.
 
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.
 
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