Page 402 - Mechatronics with Experiments

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Flow field Staticpressure

Stagnation
point, u=2
Total pressure

P
1
FIGURE 6.59: Pitot tube for
flow rate sensing via diffential
P 2 pressure measurement.

Note that Bernoulli’s equation is valid for a compressible fluid flow up to a Mach number
of about 0.2. For higher Mach numbers, the relationship can be modified and the sensor
calibrated to accurately obtain the flow speed as a function of the differential pressure and
Mach number.
As the flow passes around the Pitot tube, vortices are shed as a result of the tube
surface and fluid interaction. The frequency of the vortices is a function of the flow rate
and the pitot tube diameter. A given Pitot tube can experience a certain vortex shedding
frequency around a certain flow rate which may result in exciting the natural frequency of
the Pitot tube. Each Pitot tube sensor specification includes the range of flow rate to avoid
in order to make sure that it is not excited around its natural frequency.

Stagnation
Flow connection

Static
connection

Stationary
point

Stagnation
point

FIGURE 6.60: Pitot tube sensor picture and typical application.