Should be in the FAQ
- posted
20 years ago
Should be in the FAQ
Since no experts stepped forward, I will try to answer.
If there is supersonic flow in a tube, any disturbance, such as the needle you describe, will make a cone shaped shock wave. The shock wave will reflect off of the walls over and over again downstream.
This will also occur if the tube is just a boundary between air masses of different density. This causes the thrust diamonds sometimes visible in the supersonic exhaust of jet engines and rocket motors. As the shock waves reflect off of the cold air boundary, the waves collide in the center of the tube, heating the air to incandescence.
Supersonic wind tunnel usually have porous walls in the test section with a vacuum system to draw off air. This helps to reduce nuisance shock wave reflection off of the walls.
Lazy B Engineer
And the related answer This should be in the FAQ.
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