Quote:
Originally Posted by 3-Wheeler
The stagnation pressure *is* static pressure inside a closed duct with air flow going through it. It always takes more *pressure* either in the form of delta-P or differential to cause air to flow.
I shall mention again that the more accurate pitot tubes have *two* pressure taps.
1) One for static (pressure)
2) One for vacuum (velocity component)
The difference or delta-P between the two tells you exactly the air flow velocity of the air flowing past it.
Jim.
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That's was my whole point. The inside of the tube that points into airflow is higher pressure than the surrounding air, not lower.
http://en.wikipedia.org/wiki/Pressur...ation_pressure
Stagnation pressure is the pressure a fluid exerts when it is forced to stop moving. Consequently, although a fluid moving at higher speed will have a lower static pressure, it may have a higher stagnation pressure when forced to a standstill. Static pressure and stagnation pressure are related by the Mach number of the fluid. In addition, there can be differences in pressure due to differences in the elevation (height) of the fluid. See Bernoulli's equation (note: Bernoulli's equation only applies for incompressible, inviscid flow).
The pressure of a moving fluid can be measured using a Pitot tube, or one of its variations such as a Kiel probe or Cobra probe, connected to a manometer. Depending on where the inlet holes are located on the probe, it can measure static pressure or stagnation pressures.