Effect of stream turbulence

Подпись: (2.7)

Assuming that the motion is nearly steady and that the lateral com­ponents of turbulence are so low that they have a negligible effect on the angle of incidence, the resulting velocity U equals the sum of the average speed, U, and the fluctuating component u: the Pitot tube then reads

If velocity is constant in value but varies widely in direction, it is expected that the tube will detect a pressure lower than real because, for angles other than zero, the measured pressure is less than the stagnation pressure.

The current state of knowledge is very unsatisfactory, particularly as regards the use of Pitot tube in jets with strong turbulence, but it is hard to believe that a simple formula can give the corrections to be made to measurements in turbulent flows without knowledge of extensive data on the turbulence itself; if measures of turbulence are needed as primary data, they must be obtained with a hot wire or a laser-Doppler or a 2-focus laser anemometer.

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